So the PSU had an "x" on it, so I decided to open it up and take a look. I know the RIFA caps can be brittle and need replacing, but looking at this photos. Does it look like there is anything wrong? How would I test a PSU? Plug it in by itself, see if anything starts smoking? or is there a way to check with more deliberate steps? Here's the photos.
https://www.dropbox.com/scl/fi/e8jpqpuqq6dmcib6vh4tz/LisaPSU_3030.jpeg?rlkey=dnls1y8klu40pcerxqlglfiim&st=mdevus55&dl=0
https://www.dropbox.com/scl/fi/g0l4noxat5772kvgu24gr/LisaPSU_3031.jpeg?rlkey=2nc0zfdqzv1rl7307lej7vct9&st=5lv7mnsj&dl=0
https://www.dropbox.com/scl/fi/qd3w5lk9cnn2wvgsvn4qc/LisaPSU_3032.jpeg?rlkey=m2am60risuye6knnxqabzcz4m&st=36enfnam&dl=0
https://www.dropbox.com/scl/fi/8jbk3dfefmol28ta7g8e4/LisaPSU_3033.jpeg?rlkey=dnmno4yl7cpebqb949g8qks0x&st=iq4j3flu&dl=0
Would this be the caps needed?
Mouser #: 710-890334023011
Mfr. #: 890334023011
Mfr.: Wurth Elektroni
Safety Capacitors WCAP-FTXX 20mm Lead 0.022uF 10% 310VAC
505-MKY22W22204C00MS
Mfr. #: MKY22W22204C00MSC9
Mfr.: WIMA
Safety Capacitors 0.022 uF 20% 300V RFI Capacitor
Mouser #: 80-R46KI33300001K
Mfr. #: R46KI33300001K
Mfr.: KEMET
Safety Capacitors 275volts 0.33uF 10%
Quote from: berskyboy on August 26, 2026, 01:39:39 PMDoes it look like there is anything wrong?
The two big black main capacitors C8 & C9 appear to be bulging (tops not flat) which is a sign of impending/failure. These tend to be the PSU part that "wears out", I would replace them too.
At a glance, the replacement caps look to be appropriate, but I didn't check the pin spacing.
QuoteHow would I test a PSU?
Just plugging it in (outside of a Lisa, possibly outside of the building too if the Rifa caps are still installed) is a basic test of the integrity of the filter caps, but it doesn't test most of the PSU.
A functional test requires a load on at least +5 and +12 and a voltmeter. You can make a load with a card edge connector and power resistors or do something more fancy with a perfboard or circuitboard... some designs have been posted here and there.
With RIFAs, you just can't know in my experience: visible distress does correlate with propensity to blow up, but they do just seem liable to go at some point regardless. If I chose to power up a machine with RIFAs in it, I'd just be prepared for them to blow at any time. They probably won't permanently damage anything if they do, but they'll make a stink and a mess. These days I just replace them if I find them.
Note that in the Lisa, the computer doesn't have to be on for at least some RIFAs to have a voltage across their leads. If the Lisa is just plugged in, they are at risk of popping.
There are ways to test PSUs. For the Lisa, I have a harness with a brace of power resistors that I plug into the power connector, one resistor for each of the voltage rails, plus the ability to short the pins you need to short in order to tell the main PSU to turn on. (Note that there is also a standby power supply inside the PSU: it always provides +5V whenever the Lisa is plugged in.) The values I chose for the resistors are worked out from the minimum and maximum current draws listed in the Lisa Hardware Manual, but while the "1.2 amp" Apple-made Lisa 2/5 PSU needs some current draw to operate, I don't know if this is the case for the 1.8 amp Datapower-made 2/10 PSU that you have (maybe it can just run with no load; I've never tried it). I can share the values I use if you're interested. Anyway, once the PSU is up and running on the load, I check voltages. If they look good, then I feel good about putting the PSU back in service.
Naturally you must always be careful when working with power supplies, and note that in the 2/5 PSU at least, some of the heat sinks have quite high voltages on them. One contact can give you a good zap!
(Apologies that I can't check the capacitor choices you've listed right now!)
thanks so much. I've put in an order at DijiKey
here's a nice website / wiki with info on each part.
https://caps.wiki/wiki/Apple_Lisa_1.8A_Power_Supply_(Datapower)
Thanks for the tips on how to test it. High Voltages scare me, but that's a good thing, just be careful. :)
Quote from: stepleton on August 26, 2026, 02:26:37 PMWith RIFAs, you just can't know in my experience: visible distress does correlate with propensity to blow up, but they do just seem liable to go at some point regardless. If I chose to power up a machine with RIFAs in it, I'd just be prepared for them to blow at any time. They probably won't permanently damage anything if they do, but they'll make a stink and a mess. These days I just replace them if I find them.
Note that in the Lisa, the computer doesn't have to be on for at least some RIFAs to have a voltage across their leads. If the Lisa is just plugged in, they are at risk of popping.
There are ways to test PSUs. For the Lisa, I have a harness with a brace of power resistors that I plug into the power connector, one resistor for each of the voltage rails, plus the ability to short the pins you need to short in order to tell the main PSU to turn on. (Note that there is also a standby power supply inside the PSU: it always provides +5V whenever the Lisa is plugged in.) The values I chose for the resistors are worked out from the minimum and maximum current draws listed in the Lisa Hardware Manual, but while the "1.2 amp" Apple-made Lisa 2/5 PSU needs some current draw to operate, I don't know if this is the case for the 1.8 amp Datapower-made 2/10 PSU that you have (maybe it can just run with no load; I've never tried it). I can share the values I use if you're interested. Anyway, once the PSU is up and running on the load, I check voltages. If they look good, then I feel good about putting the PSU back in service.
Naturally you must always be careful when working with power supplies, and note that in the 2/5 PSU at least, some of the heat sinks have quite high voltages on them. One contact can give you a good zap!
(Apologies that I can't check the capacitor choices you've listed right now!)
I just replaced the RIFA Caps and the two large ones. To test it should I proceed to do what this video said?
https://www.youtube.com/watch?v=GGUZQWQytwY
Or is there another simpler way to test it? And what am I looking for. For the video it looks like measuring voltages with my multimeter is the method.
Quote from: berskyboy on September 01, 2026, 05:23:37 PMTo test it should I proceed to...
Yes, you will use a DC voltmeter to check the output voltages are within range.
(If there is a more subtle problem, an AC voltmeter may (or may not) reveal excess ripple on one of the DC voltages, but this is easier seen with an oscilloscope... it is unlikely you'll need to go this far, and not necessary to verify the PSU is safe to install in the Lisa)
The technique in the video looks fine, but if you can afford to buy a card-edge connector instead of soldering to the PSU circuit board, then it will be more convenient; eg. you will be able to test a PSU while still in the case etc.
These threads/posts may help you understand what is required:
https://lisalist2.com/index.php/topic,789.msg5772.html#msg5772
https://lisalist2.com/index.php/topic,504.msg3532.html#msg3532
Note in particular that:
- you must connect the +5 Sense to +5V, or the output voltages will rise uncontrolled.
- the interlock micro-switch must be activated
Even with the remote voltage sense, there is still a voltage drop in the card cage, so you may need to adjust the voltage to a bit more than 5V at the PSU to obtain 5V on the CPU and I/O Boards. The amount of memory, expansion cards, drives, etc. connected will affect the amount of voltage drop.
The normal supply voltage tolerance for TTL parts is 5%, so "+5" should be between 4.75V and 5.25V
Hi I connected up the four lights like this YouTube Video: https://www.youtube.com/watch?v=GGUZQWQytwY
1. no lights came on. I measured the 12V and 5V rails. They registered then drop to zero
2. I took off the lights one by one, seeing if one would light up. Leaving the 5V light, still didn't light up
3. I took off all the lights, no sounds, the 12, 5V rails do that same. They startup then go to zero
4. I measured the ohms at the 5V and 12V rails they start at 0 then climb up.
Here's a video of the board.
https://youtube.com/shorts/QDEb45ZxE3s
Images
https://www.dropbox.com/scl/fi/yzhxi7d9vpqcol9al0ukk/Lisa-PSU-Jumpers1.HEIC?rlkey=8tx6ekyhw9iecmeiflzy10nr5&st=ewgjzgu5&dl=0
https://www.dropbox.com/scl/fi/nf89dl77g8qk0zqst7ffi/Lisa-PSU-Jumper2.jpeg?rlkey=r2ivchebqohl8noumxsrp0zrc&st=ogvu8e1p&dl=0
I'm assuming I need to replace the small 5 capacitors and maybe other components. AI said check R29 but I can find that dial.
One theory is that these bulbs are drawing too much current at startup and the PSU is shutting itself down in order to protect itself from what it thinks is a shorted output. I wonder if the bulbs in the video are subtly different somehow.
When you say the other rails "registered", do you mean they briefly had the correct voltages before that voltage decayed?
Quote from: stepleton on September 02, 2026, 02:05:08 PMOne theory is that these bulbs are drawing too much current at startup and the PSU is shutting itself down in order to protect itself from what it thinks is a shorted output. I wonder if the bulbs in the video are subtly different somehow.
When you say the other rails "registered", do you mean they briefly had the correct voltages before that voltage decayed?
Yes the rails had the correct voltage then down to zero. The bulbs are 13v, I bought from a car shop, they are standard 12-Volt miniature automotive bulbs
Quote from: berskyboy on September 02, 2026, 02:13:04 PMThe bulbs are 13v, I bought from a car shop, they are standard 12-Volt miniature automotive bulbs
Note that at timestamp 3:16 in the european (I think) video he says the two bulbs in series are 24V
each, while the other two are 12V.
If you are using all 12V bulbs, you'd want at least 3 in series for the 33V supply. However, I don't think the 33V supply absolutely has to have a load to start up the PSU, so I'd first try just disconnecting those to see if the PSU will start up.
More importantly, the video shows the PSU has one white jumper installed (on the top side) for 220V, does yours have the 3 jumpers installed for 110V?
edit: I see in your video of the top side that you do have the jumpers installed for the 110V configuration.
edit 2: at timestamp 0:40 in your video I see a loose lockwasher... remove it as you don't want it relocating and causing a short circuit as that may damage multiple components.
edit 3: are the symptoms still repeatable? If not, check if the fuse has blown
edit 4: R29 is in the video brightness circuit, this is not connected to the power supply circuitry itself so doesn't affect it powering up outside the Lisa.
Re: measuring the resistance at the output of a PSU:
- If the PSU is powered up, or has significant charge on the filter capacitors from being powered up recently, the ohmmeter may be damaged.
- It is normal for the resistance to start at 0 and rise, this is due to the current from the ohmmeter quickly then slowly charging the filter cap you have connected to.
I have removed that lock washer. (Thanks for that)
I remove the jumper wires tested, 0V
then I re-added them and getting 5V then goes to zero, and 11.5 V then to zero.
it makes a quiet shhhhhh sound (like when you would tune a radio), but very faint, and then off.
So do I need to start replacing components? It seems it does produce power, but then shuts off.
This is my DijiKey List. (Note I already replaced the RIFA caps and the two large Capacitors)
https://www.digikey.ca/short/nqwvwb17
Quote from: berskyboy on September 02, 2026, 03:57:20 PMdo I need to start replacing components? It seems it does produce power, but then shuts off.
I recommend not blindly replacing components, at least not yet. It is very likely that after replacing many components it would still not work.
I'll look over your photos to see if the way it was wired has any obvious problems.
Given that it seems to almost work, it is probably possible to narrow down the problem substantially, but it will take some time/patience and back and forth measuring things.
edit: what is the wattage or current rating of the 12V bulbs you are using? (or their part number if the wattage isn't specified)
edit 2: the bottom of the board shows a couple of dark patches (scorch marks), what are the component designations that correspond to these? For example, it looks like R3 beside the white jumpers is one of the components that is getting hot (which is normal, but maybe not the others).
The bulbs are 4057LL.Bp2 LAMP Bulb
https://www.canadiantire.ca/en/pdp/4057-sylvania-long-life-mini-bulb-2-pk-0202857p.0202857.html?utm_content=shopping&gclsrc=aw.ds&gad_source=1&gad_campaignid=24075369818&gbraid=0AAAAADojZpheGGp8Mr_9WqX3o-9pEnlse&gclid=Cj0KCQjwkt_UBhDMARIsALpnOAxAAhAfH3vqS6Pp_CuVl7QJVEUvGO24I8ThIRwVkpKtLZZqC1Ge5EQaAlpCEALw_wcB#store=397
12.8V 14V, but maybe the WATTS are wrong. LOL
Also more photos of the bottom and the top
https://www.dropbox.com/scl/fi/8odk8cynrm5y4n206e9s6/Lisa-PSU1.jpeg?rlkey=e7wxzctih90zpu8tfi8b8m7vn&st=lsr47ej6&dl=0
https://www.dropbox.com/scl/fi/1pee4kbx8o6ngpqj72rrr/Lisa-PSU3.jpeg?rlkey=5tjltsf7o0nbmp3f5drsvw991&st=ch6ec0we&dl=0
https://www.dropbox.com/scl/fi/bh635l9pnbfii2qoyahym/Lisa-PUS2.jpeg?rlkey=a1zrhnlz8vfoho1xpzyvnk1yw&st=nd3ey7ft&dl=0
AI told me to go with resisters vs bulbs,
4. High-Wattage Dummy Load Resistors (To replace your bulbs)
What they do: To permanently graduate from the light bulb trap—which keeps triggering your over-current latch due to cold inrush current—you need true resistive loads.
What to order:One 2 Ohm, 25-Watt or 50-Watt aluminum-housed chassis mount resistor (for your +5V rail)One 12 Ohm, 25-Watt aluminum-housed chassis mount resistor (for your +12V rail)
Quote from: berskyboy on September 02, 2026, 05:55:11 PMThe bulbs are 4057
12.8V 14V, but maybe the WATTS are wrong. LOL
Those are dual filament bulbs for tail lights. They have a dim filament for the parking/running lights and a bright filament for the brake light.
The two power ratings of 27W and 6.7W correspond to the bright and dim filaments. Using the common formula P = V*V/R, we can calculate the resistance to see how much current they will draw when connected to a different voltage such as 5V.
The bright filament is 27W at 12.8V -> 6 ohms
The dim filament is 6.7W at 14V -> 29 ohms
So connecting the bright filament to 5V, you'll draw about 0.8 Amps, which is not very much for that power supply.
I'm supposing that if you have/had connected the dim filaments, that wasn't enough load for the PSU to start up. You can use your ohmmeter to check which filament is connected, or you may be able to tell by looking through the glass. The dim filament is a longer length (more coils) of thinner wire.
QuoteAI told me to go with resisters vs bulbs,
4. High-Wattage Dummy Load Resistors (To replace your bulbs)
What they do: To permanently graduate from the light bulb trap—which keeps triggering your over-current latch due to cold inrush current—you need true resistive loads.
What to order:One 2 Ohm, 25-Watt or 50-Watt aluminum-housed chassis mount resistor (for your +5V rail)One 12 Ohm, 25-Watt aluminum-housed chassis mount resistor (for your +12V rail)
Thanks for pointing out that is suggested by AI... it is important that we keep tabs on the sort of information it provides!
For this particular application, the inrush current is probably not an issue, as 1980's digital electronics will also have a high inrush current.
The recommendation of single aluminum power resistors is not cost-conscious. Those are appropriate when saving space, which isn't normally an issue for a test jig. Cost goes up rapidly with power capability, and goes down with quantity, so 5 5 watt resistors is often much cheaper than 1 25 watt resistor. In addition, by spreading the load among multiple resistors, they probably won't be as hot.
As for the values suggested, 2 ohms on a 5V supply will draw 2.5 Amps and dissipate 12.5 watts. Doubling the power capability to 25W is derating the resistor to extend its life, but for the few minutes it will be in use, that's not necessary here. Increasing further to 50W is multiplying the cost substantially.
The 12 ohm load on 12V would draw 1A and 12W.
Suggestion: double check that you have the bright filaments connected as loads to the +12 and +5 voltages, and see if it behaves any differently.
I am able to get a Lisa DataPower PSU to start up with a 30 ohm load on +12 and a 9 ohm load on +5, anything less than that shuts down promptly. I only tested one unit - others may be a bit different.
So if using 6 ohm brake light bulbs, one is likely to be sufficient for each of +12 and +5; 29 ohms may work for +12, but not +5.
I suppose one dual filament bulb might be sufficient if the dim filament was connected to +12 and the bright filament connected to +5.
Note that these are light loads compared to a normally configured Lisa, so the voltages output could be outside of normal specifications, but if close-ish, eg. within 10% of nominal, I'd suppose it was safe to install in a real Lisa. (If still in doubt, remove any extra boards/drives so as to not risk more components than necessary.)
With no load on the 33V line, it would likely read somewhat higher than +10%. edit:
with no load, it may float very high, above the 50V rating of the filter capacitor, some some load is recommended.Once the Lisa is running, check the +5 voltage on the I/O Board and adjust the PSU to get 5V +/- 5% (4.75 - 5.25V).
IIRC, the DataPower voltage adjustment (R11 on the PSU daughterboard) is counter-clockwise to increase.
edit:
The Hardware Reference Manual says that the original Lisa Power Supply (aka the "1.2 Amp" variety) is rated as follows (although, note the manual doesn't necessarily reflect the hardware as manufactured):
| Volts | Amps |
| +5 | 8.0 |
| -5 | 0.2 |
| +12 | 2.0 |
| -12 | 0.2 |
| +33 | 0.6 |
| +5 Stby | 0.1 |
The DataPower PSU (aka the "1.8 Amp" variety) probably has higher ratings, but are unspecified AFAIK.
Hi,
I ordered 7 of the little caps and a dummy load.
It powers up shows 5V then zero, and the other rail 7-8V then zero
here's a photo of my shenanigans
https://www.dropbox.com/scl/fi/cqwv7x3u49sj5sipfc4uw/Lisa-with-Dummy-Load.HEIC?rlkey=du47osr524mfqqnb1n58igijy&st=26thql5v&dl=0
AI told me to replace the following:
- 296-49723-ND
LM393PE3
Texas Instruments
IC COMPARATOR 2CH 8-PDIP
(here at DijiKey): https://www.digikey.ca/en/products/detail/texas-instruments/LM393PE3/2596857
- 4N35MLT-ND
4N35M
LITEON
OPTOISO 3.55KV TRANS W/BASE 6DIP
(here at DijiKey): https://www.digikey.ca/en/products/detail/liteon/4N35M/388380
I can't see where to put this one, but wanted to get more info from the group
thanks
Quote from: berskyboy on September 04, 2026, 09:23:54 PMhere's a photo of my shenanigans
Thanks for the update - can you post a pic of the current wiring on the other side?
QuoteI ordered...
With your next order, please get a card-edge connector so that the wiring is more easily seen/verified.
For the Lisa PSU, that is 0.156" pitch, dual row aka dual readout, 22/44 positions, with solder eyelets for a 0.062" thick circuit board.
eg. https://www.digikey.ca/en/products/detail/edac-inc/355-044-500-202/1295268 (https://www.digikey.ca/en/products/detail/edac-inc/355-044-500-202/1295268)
If you don't have a junk-box with scavenged/spare parts where you can find a free one, you might also get a switch that you can use to turn on/off the PSU (acting like the signal from the I/O Board & soft switch).
eg. https://www.digikey.ca/en/products/detail/adam-tech/SW-T3-1A-A-A3-S1/15284460 (https://www.digikey.ca/en/products/detail/adam-tech/SW-T3-1A-A-A3-S1/15284460)
Those two parts suggested as among the lowest cost of what is currently in stock at DigiKey, there are lots of alternative parts that will work if those are out of stock. You could even use a household wall switch if you have one of those.
QuoteAI told me to replace the following:
LM393PE3
IC COMPARATOR 2CH 8-PDIP
4N35M
OPTOISO 3.55KV TRANS W/BASE 6DIP
I can't see where to put this one, but wanted to get more info from the group
AI is hallucinating, the Lisa PSU doesn't have an optoisolator and replacing the LM393 is very unlikely to be the solution in this case.
Keep in mind that desoldering parts isn't like disassembling something mechanical. It is easy to damage a circuit board (delaminating the fibreglass, lifting traces, etc.), and the damage accumulates, so replacing parts that don't need replacing may result in creating an unreliable end-result or even scrapping the board entirely.
Quote from: sigma7 on September 05, 2026, 01:48:36 AMWith your next order, please get a card-edge connector so that the wiring is more easily seen/verified.
For the Lisa PSU, that is 0.156" pitch, dual row aka dual readout, 22/44 positions, with solder eyelets for a 0.062" thick circuit board.
eg. https://www.digikey.ca/en/products/detail/edac-inc/355-044-500-202/1295268 (https://www.digikey.ca/en/products/detail/edac-inc/355-044-500-202/1295268).
If you don't have a junk-box with scavenged/spare parts where you can find a free one, you might also get a switch that you can use to turn on/off the PSU (acting like the signal from the I/O Board & soft switch).
eg. https://www.digikey.ca/en/products/detail/adam-tech/SW-T3-1A-A-A3-S1/15284460 (https://www.digikey.ca/en/products/detail/adam-tech/SW-T3-1A-A-A3-S1/15284460)
Those two parts suggested as among the lowest cost of what is currently in stock at DigiKey, there are lots of alternative parts that will work if those are out of stock. You could even use a household wall switch if you have one of those.
I have this in my BOM at DijiKey. (I added the capacitor as I ordered a wrong part the first time)
(how will I use this CONN EDGE DUAL FMALE 44POS?)
https://www.digikey.ca/short/b4rwqz2f
Here's a recent photo.
https://www.dropbox.com/scl/fi/zkmb2xrtpdenb2k7mu5gr/LisaPSU-Bottom-2026ASept05.jpeg?rlkey=eli19l3jrqhjdj9ih26ed0dnq&st=kf66l5zm&dl=0
https://www.dropbox.com/scl/fi/rnek80a8q0bm78civyp5p/LisaPSU-Top-2026ASept05.jpeg?rlkey=q69vo78b9po0hzs3xg4zmwm3p&st=8lxcjac4&dl=0
(I recapped all the caps that are missing)
https://www.dropbox.com/scl/fi/b5x7w6wy0jsux7xby6pm6/LisaPSU-Top-2026ASept05b.jpeg?rlkey=x3mmfyvw11bjlz7mqts2biw2h&st=s2g4mbwk&dl=0
I had a short after reflowing all the joints on the bottom. I have new fixed that and getting 5V then zero and 7-8V then zero on the 12V rail. I think the replacement cap coming will fix the 12V rail.
I did rejumper the jumpers wires too
Quote from: berskyboy on September 05, 2026, 11:23:25 AMhow will I use this CONN EDGE DUAL FMALE 44POS?
Your PSU under test will plug into the new edge connector (it is the same connector as inside the Lisa chassis). You will attach the switch and load resistors to the edge connector rather than soldering wires directly to the PSU. Some advantages are that you can replace components without jumper wires in the way, access all the output voltages, see the load wiring from the top, and so on.
QuoteI did rejumper the jumpers wires too
Please post a picture showing the current wiring... the wires disappear under the board in the latest pictures.
Here are some things to check - please ask questions if anything is unclear:
Unplug the power supply and wait 5 minutes.
Check the DC voltage across R33 (from one end to the other, not to ground) & across R2. (These are two large resistors beside the large black capacitor C8.)
If they are not below 0.1 VDC, wait longer.
Once the voltages are below 0.1 VDC:
Detach the load resistors (one lead of each is sufficient, you can leave one lead connected or remove entirely)
Put your digital multi-meter (DMM) into the "Diode Test" mode.
Locate CR22 along the top edge of the board. Put the Red DMM probe on the top lead of CR22 (the end with the light coloured band) and the Black DMM probe on the bottom lead of CR22. Once the display settles, the DMM should indicate open-circuit (same display as when your DMM probes are not touching anything). Reverse the probes so black is on top and red is on the bottom of CR22. When the display settles, the reading should be around 0.4 V.
Repeat for CR21 beside it, expecting very similar readings.
Check CR23 and CR25 in the same way, these two should show around 0.4V in one direction and a bit less than 0.4V in the other.
Check CR24 and CR26 with red on the bottom and black on top. Each of these should settle to about 0.4 V. You can try the other direction, but it will take a long time for the voltage to settle since they have big capacitors attached, if the voltage increases past about 0.5V then you can stop waiting; we're looking to confirm it isn't 0.0V indicating a shorted diode.
Locate CR20, which is a big silvery component (often marked NSD3040) with a cylindrical top on a black heatsink. With the red lead on ground and the black lead on the metal case of CR20, the DMM should settle around 0.1 or 0.2 V (not 0.0V). If you reverse the leads, the reading should start low and increase... you may remove the leads when you reach 1V or so, you don't need to wait for it to settle; we just want to make sure it isn't near 0V.
Return your DMM to the DC Voltage mode if that is separate from the On/Off switch.
Report your findings.
... continuedAssuming nothing suspicious was found checking the diodes above (ask if you're not sure), proceed with these live measurements:
1. Connect the +5, +12, and +33 loads, making sure that "+5 Sense" is connected to the +5V output.
2. If your test setup has an on-off switch to control the PSU, set it to the off position.
3. Plug in the PSU... be careful what you touch as there is now line voltage present on the board.
4. Check the DC and AC voltages from pin 3 of the daughterboard connector to ground. This should be about 16 to 18V DC, and should have an AC voltage of less than 1V. If the DC voltage is about half or double, remove power and investigate whether the 115/230V jumpers are not installed correctly or damaged or not making proper contact. If the voltage is zero, check the fuse. Remember to set the meter back to DC volts after measuring the AC volts.
5. Check the DC voltage across R33 (from one end to the other, not to ground) & across R2. (These are two large resistors beside the large black capacitor C8.) They should be about 150-170 V each (positive or negative, depending on which way you probe them). If not, then the primary rectifier, line filter, and associated components are suspect.
6. Check the DC voltage at pin 12 of the daughterboard connector to ground. This should be about 5V. If not then Z2 on the daughterboard is suspect.
7. If your test setup has an on-off switch to control the PSU, set it to the On position. Make sure the interlock switch has been engaged.
8. Check the +5 and +12 output voltages. If they are close to those values, then what follows is the wrong troubleshooting procedure... this is for the case where those voltages are close to zero (perhaps after briefly being at the correct voltage).
9. Check the DC voltage at pin 8 of the daughterboard connector to ground. If this is low (around 0 VDC), then some part of the circuit is telling the PSU not to run. That could be the interlock switch, the +12V overvoltage crowbar on the main board, the +5 or +12 voltage sense on the daughterboard, the over-current sense on the daughterboard, or the soft-power control circuit. If it is high (around +5 VDC), then the daughterboard is attempting to run the PSU.
10. Check the DC voltage at pin 13 of the daughterboard connector to ground. If this is low (around 0 VDC), then the brownout detect is telling the PSU the voltage is not high enough to turn on, or it thinks the soft power switch is indicating turn-off.
11. Carefully (be careful the probe does not slip and cause a short circuit) check the voltage at the + side of C14 on the daughterboard. If low (around 0 VDC), then the brownout circuit is suspect.
12. Carefully (be careful the probe does not slip and cause a short circuit) check the voltage at the lower end of R30 on the daughterboard, if high (around 5 VDC) then the soft-power circuit is suspect.
Report your findings.
Note this is a new troubleshooting procedure description, so there may be errors. We will double check conclusions and discern further steps depending on what you find.edit: clarified resistor location, typo
edit 2: continuation
edit 3: clarified DMM, "high" & "low" voltages
edit 4: added reference to +33 load
Quote from: berskyboy on September 05, 2026, 11:23:25 AMHere's a recent photo.
https://www.dropbox.com/scl/fi/b5x7w6wy0jsux7xby6pm6/LisaPSU-Top-2026ASept05b.jpeg?rlkey=x3mmfyvw11bjlz7mqts2biw2h&st=s2g4mbwk&dl=0 (https://www.dropbox.com/scl/fi/b5x7w6wy0jsux7xby6pm6/LisaPSU-Top-2026ASept05b.jpeg?rlkey=x3mmfyvw11bjlz7mqts2biw2h&st=s2g4mbwk&dl=0)
The pictures show that at least one of the trimmer potentiometers (R11) on the daughterboard is askew. I suspected this is just a manufacturing slip, but now wondering if it may indicate that it suffered some trauma or other misadventure, breaking something (either a trace or solder joint on the circuit board, or the potentiometer itself).
I don't think we've seen a picture of the back of the daughterboard, so:
- please post a pic of the back of the daughterboard so we can look for damage, and
- wiggle the trimmer potentiometers to see if they are rigidly attached to the board or at all loose.
Quote from: sigma7 on September 06, 2026, 06:22:52 PMQuote from: berskyboy on September 05, 2026, 11:23:25 AMHere's a recent photo.
https://www.dropbox.com/scl/fi/b5x7w6wy0jsux7xby6pm6/LisaPSU-Top-2026ASept05b.jpeg?rlkey=x3mmfyvw11bjlz7mqts2biw2h&st=s2g4mbwk&dl=0 (https://www.dropbox.com/scl/fi/b5x7w6wy0jsux7xby6pm6/LisaPSU-Top-2026ASept05b.jpeg?rlkey=x3mmfyvw11bjlz7mqts2biw2h&st=s2g4mbwk&dl=0)
The pictures show that at least one of the trimmer potentiometers (R11) on the daughterboard is askew. I suspected this is just a manufacturing slip, but now wondering if it may indicate that it suffered some trauma or other misadventure, breaking something (either a trace or solder joint on the circuit board, or the potentiometer itself).
I don't think we've seen a picture of the back of the daughterboard, so:
- please post a pic of the back of the daughterboard so we can look for damage, and
- wiggle the trimmer potentiometers to see if they are rigidly attached to the board or at all loose.
Hi Sigma7, I did order the parts from DijiKey, but in the meantime here's the photos of my daughter board.
https://www.dropbox.com/scl/fi/cno0vcd618l7x5om0bj45/LisaPSU-Daugher1.jpeg?rlkey=f6jctwfti5tmbdklgnbu3mpk8&st=o711m088&dl=0
https://www.dropbox.com/scl/fi/q08payw5ehw7si9gln1hw/LisaPSU-Daugher2.jpeg?rlkey=n6oanpg7c4rkdthew3ibv3f0p&st=cokxhfes&dl=0
2. They seem solid. I was using a screwdriver to adjust some of the values and they were moving.
Quote from: sigma7 on September 05, 2026, 03:26:58 PMQuote from: berskyboy on September 05, 2026, 11:23:25 AMhow will I use this CONN EDGE DUAL FMALE 44POS?
Detach the load resistors (one lead of each is sufficient, you can leave one lead connected or remove entirely)
is this R33 and R2? detaching, them measuring the diodes. When do I reattached these resistors? Or NOT yet, continue with steps 1-12?
Quote from: berskyboy on September 06, 2026, 09:45:00 PMQuote from: sigma7 on September 05, 2026, 03:26:58 PMDetach the load resistors (one lead of each is sufficient, you can leave one lead connected or remove entirely)
is this R33 and R2? detaching, them measuring the diodes. When do I reattached these resistors? Or NOT yet, continue with steps 1-12?
In this case, the load resistors are the light bulbs or aluminum housed power resistors or the like that are external to the PSU. ie. they are resistors that are not permanently part of the PSU. They simulate the load that is presented by the real Lisa hardware when the PSU is installed in the chassis.
You need to disconnect the external load resistors to check the diodes as they will affect those measurements.
After checking the diodes, you attach the load resistors in step 1 of the second part: "Connect the +5, +12, and +33 loads, making sure that "+5 Sense" is connected to the +5V output."
Quote from: berskyboy on September 06, 2026, 09:30:58 PMhere's the photos of my daughter board
https://www.dropbox.com/scl/fi/q08payw5ehw7si9gln1hw/LisaPSU-Daugher2.jpeg?rlkey=n6oanpg7c4rkdthew3ibv3f0p&st=cokxhfes&dl=0
The circle in the attached pic. is around what looks like it may be a broken solder joint.
Put a finger on the questionable solder joint, and wobble the body of the potentiometer to see if you can feel the joint moving.
Regardless of whether you can feel anything moving, resolder the 3 legs of that potentiometer.
Ideally, you would desolder the 3 legs, fully seat the potentiometer against the board, and resolder. This would reduce the chance of the same thing happening again.
Quote from: sigma7 on September 06, 2026, 10:53:51 PMQuote from: berskyboy on September 06, 2026, 09:45:00 PMQuote from: sigma7 on September 05, 2026, 03:26:58 PMDetach the load resistors (one lead of each is sufficient, you can leave one lead connected or remove entirely)
is this R33 and R2? detaching, them measuring the diodes. When do I reattached these resistors? Or NOT yet, continue with steps 1-12?
In this case, the load resistors are the light bulbs or aluminum housed power resistors or the like that are external to the PSU. ie. they are resistors that are not permanently part of the PSU. They simulate the load that is presented by the real Lisa hardware when the PSU is installed in the chassis.
You need to disconnect the external load resistors to check the diodes as they will affect those measurements.
After checking the diodes, you attach the load resistors in step 1 of the second part: "Connect the +5 and +12 loads, making sure that "+5 Sense" is connected to the +5V output."
OK that makes sense. And should I have those jumper wires also connected when doing the diode tests. And reload the dummy load and jumper wires for test 1-12 for live measurements. (I think the parts I bought from DijiKey should make adding those loads and the jumper wires much easier and I can put jumper wires to the male connectors of the Card Edge Connectors).
Quote from: sigma7 on September 06, 2026, 11:02:17 PMQuote from: berskyboy on September 06, 2026, 09:30:58 PMhere's the photos of my daughter board
https://www.dropbox.com/scl/fi/q08payw5ehw7si9gln1hw/LisaPSU-Daugher2.jpeg?rlkey=n6oanpg7c4rkdthew3ibv3f0p&st=cokxhfes&dl=0
The circle in the attached pic. is around what looks like it may be a broken solder joint.
Put a finger on the questionable solder joint, and wobble the body of the potentiometer to see if you can feel the joint moving.
Regardless of whether you can feel anything moving, resolder the 3 legs of that potentiometer.
Ideally, you would desolder the 3 legs, fully seat the potentiometer against the board, and resolder. This would reduce the chance of the same thing happening again.
OK, I will resolder those potentiometer. I did a resolder of the main board yesterday also. Once I do that I will re-send the photos of the bottoms of both cards.
Quote from: berskyboy on September 06, 2026, 11:13:39 PMshould I have those jumper wires also connected when doing the diode tests. And reload the dummy load and jumper wires for test 1-12 for live measurements. (I think the parts I bought from DijiKey should make adding those loads and the jumper wires much easier and I can put jumper wires to the male connectors of the Card Edge Connectors).
I believe the jumper wires for the soft power switch and the +5 Sense shouldn't affect the diode check, so you could leave those.
Yes, being able to plug and unplug everything at once with the card-edge connector is convenient.
Quote from: sigma7 on September 05, 2026, 03:26:58 PMQuote from: berskyboy on September 05, 2026, 11:23:25 AMhow will I use this CONN EDGE DUAL FMALE 44POS?
Locate CR22 along the top edge of the board. Put the Red DMM probe on the top lead of CR22 (the end with the light coloured band) and the Black DMM probe on the bottom lead of CR22. Once the display settles, the DMM should indicate open-circuit (same display as when your DMM probes are not touching anything). Reverse the probes so black is on top and red is on the bottom of CR22. When the display settles, the reading should be around 0.4 V.
Here's the readings if I've done CR22 correct
https://www.dropbox.com/scl/fi/8cwfuee42nvnn3gwvw3gl/CR22_1.jpeg?rlkey=iqhlzg6a3wwvir2uvbpd66eez&st=914epwqo&dl=0
https://www.dropbox.com/scl/fi/766m25yt8jibe72yms6t5/CR22_2.jpeg?rlkey=stnxp2q8b6perldu17kkq3ayz&st=gys6p8mv&dl=0
https://www.dropbox.com/scl/fi/o7p1vgwum3edotlcs5z70/CR22_3.jpeg?rlkey=lkrds1cduqm576b4d6rdca0pf&st=pbi8eb84&dl=0
CR23
https://www.dropbox.com/scl/fi/ceeth99alhm5w0zqqqkoe/CR23_1.jpeg?rlkey=ejej1etyeiv5w3nlpyjxg687o&st=3pvwxm28&dl=0
https://www.dropbox.com/scl/fi/p40kxcrnsrrluxfh2jwlm/CR23_2.jpeg?rlkey=rsyxfm0ivitw0wfvj6fba7x7i&st=0t26p1jh&dl=0
and the rest of the CR values in the area
https://www.dropbox.com/scl/fi/q310mpvrycrgaetpg9xwf/Other-CR-Values.HEIC?rlkey=ivho0ghzd6zv8odqe188ha8bj&st=bcz8m4hz&dl=0
so it seems like CR23 and CR25 have values other than 1 (458 and 536)
CR20
https://www.dropbox.com/scl/fi/oapr7jy1eamhjydykcu42/CR20.HEIC?rlkey=3iyh3xovugcqohuh9ddxaqcic&st=ol29exls&dl=0
and climbs with the leads on the opposite polarity.
Quote from: berskyboy on September 07, 2026, 01:23:33 PMHere's the readings ...
Everything looks fine there.
Your particular DMM has a couple of quirks:
For the diode test at least and probably resistance too, "Out of range" or "Open Circuit" is shown as a "1" at the left with no other indicators lit.
For the diode test, the decimal point is not shown, so the display shows "461" when the measurement is 0.461 V.
This isn't unique to your brand of DMM, and other brands have different ways of showing the same thing.
Quote from: sigma7 on September 07, 2026, 02:53:51 PMQuote from: berskyboy on September 07, 2026, 01:23:33 PMHere's the readings ...
Everything looks fine there.
Your particular DMM has a couple of quirks:
For the diode test at least and probably resistance too, "Out of range" or "Open Circuit" is shown as a "1" at the left with no other indicators lit.
For the diode test, the decimal point is not shown, so the display shows "461" when the measurement is 0.461 V.
This isn't unique to your brand of DMM, and other brands have different ways of showing the same thing.
So I've put the new capacitor into C24 with higher voltage (CAP ALUM 4700UF 20% 35V RADIAL), and put the edge connector and now it's doesn't do anything when turning on, but when I turn it off, it makes a noise and stays at 0.5V. Here's a video of it all
Any help would be amazing. I'm even thinking of shipping it to someone to fix?
https://www.youtube.com/shorts/OFgUFjGKWMQ
Quote from: berskyboy on September 09, 2026, 05:56:09 PMhelp would be amazing
Your card edge connector isn't wired correctly, see annotated pic. below.
Many of the wires shown are soldered to both the top row and bottom row of the connector. This is not necessary, but it is important that +5 Sense (Pin 'N') is connected to +5V in some manner.
The components in the pic are mounted to a "perf-board", this isn't necessary but makes the jig more durable.
The +5 load is shown connected with 2 red wires, one is sufficient unless it is very thin.
The 33V load shown on the left (three 910 ohms @2W resistors in parallel) is
optional recommended even for basic testing.
The +5 load shown is 1 ohm @50W, which is more of a load than necessary for basic testing (and an expensive resistor), and a heavier load than a typical Lisa. The PSU will run with a +5V load up to around 9 ohms.
The +12 load shown is 10 ohms @10W in series with 5.1 ohms @5W (making 15.1 ohms @ 15W), which is more of a load than necessary for basic testing. The PSU will run with a +12V load up to around 30 ohms.
edit: changed recommendation for +33 load
Quote from: sigma7 on September 09, 2026, 06:09:21 PMYour card edge connector isn't wired correctly, see annotated pic. below.
Ok, sounds good. I purchased a prototype board (like your photo) and will build that tomorrow. Thanks
Quote from: sigma7 on September 09, 2026, 06:09:21 PMQuote from: berskyboy on September 09, 2026, 05:56:09 PMhelp would be amazing
Your card edge connector isn't wired correctly, see annotated pic. below.
Many of the wires shown are soldered to both the top row and bottom row of the connector. This is not necessary, but it is important that +5 Sense (Pin 'N') is connected to +5V in some manner.
The components in the pic are mounted to a "perf-board", this isn't necessary but makes the jig more durable.
The +5 load is shown connected with 2 red wires, one is sufficient unless it is very thin.
The 33V load shown on the left (three 910 ohms @2W resistors in parallel, making 303 ohms @ 6W) is optional recommended even for basic testing.
The +5 load shown is 1 ohm @50W, which is more of a load than necessary for basic testing (and an expensive resistor). The PSU will run with a +5V load up to around 9 ohms.
The +12 load shown is 10 ohms @10W in series with 5.1 ohms @5W, which is more of a load than necessary for basic testing. The PSU will run with a +12V load up to around 30 ohms.
This is a picture of my video/picture of my setup
Not getting any more volts,
https://www.dropbox.com/scl/fi/j46gt0ha2u9smh5ja6qhf/Edge-Connector1.jpeg?rlkey=ieaoxo32ysnqnndps408uwwuy&st=ypednpch&dl=0
https://www.dropbox.com/scl/fi/vnmj2s72pa9wj4ihqlqu2/Edge-Connector2.jpeg?rlkey=kn6rlkohv8dfiz85ybkv92hew&st=7nu2p9jr&dl=0
sigma7 edit: made +33 load recommended
Quote from: berskyboy on September 09, 2026, 11:38:35 PMThis is a picture of my video/picture of my setup
The PSU won't "turn on" unless pins 20 and "X" are connected to each other. In my photo above, they are connected via the little toggle switch on the right (note the orange text) so one can turn it on and off like the I/O Board does (aka "Soft Power") using the switch.
If you purchased the switch (or have one), wire it to pins 20 and "X". If you don't have a switch, connect the two pins with a wire and the PSU will turn on as soon as you plug it in.
Having the on/off switch will make it easier to troubleshoot logic problems on the daughterboard, as that allows you to connect the voltmeter to various points and observe what happens the moment the PSU "turns on" (and then decides to turn itself off).
(In this case, "turn on" is not the same as connected to the mains/110V via the power strip)
(I don't think you need to order any more parts, my guess is that the broken solder joint on the potentiometer was the problem, and once you get the test setup going, the rest will be quick... could be wrong though.)
edit: The pictures in your last post don't all show the same wiring, which makes it hard to point out what you need to change (since it is different for each picture). In summary, for the PSU to turn on (so you get +5V and +12V), you need to have all of these connections at the card edge at the same time:
- Connect a load from +5 to ground
- Connect a load from +12 to ground
- Connect +5 Sense to +5V
- Connect the "On" signal Pin "X" to +5Standby Pin 20 (perhaps through the little switch)
If any of those are missing, the PSU won't turn on (except momentarily perhaps). You should also have a +33 load, but the PSU will still power up without it.
edit: Your wires are not too small for a quick test... when they are too small and you run it too long, they will get hot and perhaps the insulation will start to melt or smoke. If you are concerned, you can double them up or use bigger wire.
It is very unlikely the new parts are bad if purchased from a reputable supplier such as DigiKey, Mouser, Newark/Element14. Once you get the PSU turned on, if there is a problem with a capacitor, we can diagnose that issue.
Quote from: sigma7 on September 09, 2026, 11:52:27 PMedit: The pictures in your last post don't all show the same wiring, which makes it hard to point out what you need to change (since it is different for each picture). In summary, for the PSU to turn on (so you get +5V and +12V), you need to have all of these connections at the card edge at the same time:
- Connect a load from +5 to ground
- Connect a load from +12 to ground
- Connect +5 Sense to +5V
- Connect the "On" signal Pin "X" to +5Standby Pin 20 (perhaps through the little switch)
Morning, so I put the switch onto pin 20 (before I get my protype board today) and it showed 9V or something like that, and it stayed on. I turned it off still showing about 9V. So it appears to stay on. But as time s goes on it goes down. Then measure 5V, then 4V. But doesn't drop immediately. I was playing with the potentiometer (both of them on the daughter board). So it seems from a cold start, rest overnight, it has power, then less and less as you test? I will test it again in couple of hours to see.
Here's the photos of my edge connector
https://www.dropbox.com/scl/fi/q1xcrm974er25hmfr8kb9/PSU-2026Sep1001.jpeg?rlkey=5kbp30viejm71ktbfbtx944eu&st=mpp7fi9t&dl=0
https://www.dropbox.com/scl/fi/kt1z55x3sf6nd0kgp8l1n/PSU-2026Sep1002.jpeg?rlkey=zarq5ak8fhy521mmi7v4ut9qs&st=qo788y97&dl=0
thanks for all your help troubleshooting!
UPDATE: I got it working after 2 hours and it stayed at 11v on the 5v rail, nothing on the 12V rail. Then a flash by the daughter board, and a blowed fuse.
https://www.dropbox.com/scl/fi/i2vnj5lw3wmkqbwxt4vgg/Fuse01.jpeg?rlkey=jo950szucveuo72xsbre0xhfq&st=13h71jph&dl=0
https://www.dropbox.com/scl/fi/nydhs975oo1m3i1gwfvtf/Fuse02.jpeg?rlkey=pwuehcrdv4ex6h158o0qhpjrx&st=ni6eyth7&dl=0
Video
https://youtube.com/shorts/66k2mwcBKhw
I'm off to get a 3A 250V fuse. But will check for shorts, maybe do some soldering touchups before trying to turn it on again. (And I will assemble my prototype board)
Quote from: berskyboy on September 10, 2026, 09:30:00 AMHere's the photos of my edge connector
UPDATE: I got it working after 2 hours and it stayed at 11v on the 5v rail, nothing on the 12V rail. Then a flash by the daughter board, and a blowed fuse.
Hopefully the flash was from the fuse. If you replace the fuse without locating the reason it blew, then it will just blow again, so don't apply power until the reason is found and corrected.
The 5V output should never be above ~ 5.5V as that is a fault that could damage much of the computer (if the PSU had been installed in one). If you see that happen again, remove power immediately.
In the picture, it isn't clear if the wire attached to pin 12 is actually touching/soldered to the pin "N" below it. Rather than just fixing it, check the resistance between the pins with the DMM. If the resistance is high, then that confirms they aren't properly connected and that is likely the cause of the excessively high 5V and possibly blowing the fuse. If it is low resistance then you need to look for another fault...
Do not connect to power until a fault is found and corrected otherwise more damage may result.
Examine the board carefully, looking for signs that a capacitor has physically deformed, or signs of burns/scorch marks on the circuit board, resistors, and other components. Signs of overheating include browned or charred components, and you may be able to localize such damage by odour as well as appearance. Your recent pictures may be helpful to identify changes. If you find a damaged component, assume that is another consequence of the fault, not the fault itself. Locating damaged components will help determine where the fault is.
Check the bottom of the board too. See if the position of the board may have shifted, causing a short circuit to whatever is beside or under it. (In an earlier picture, part of the metal enclosure looked like it was partially under the circuit board without insulation or constraint, but one can't easily tell in a 2D picture if they are too close.)
When the PSU is operating, even briefly, the filter capacitors are charged and once power is removed they slowly discharge. This is why the voltage you measured was decaying over time. The voltage across capacitors that have bleed resistors (such as R33 & R2) will decay more rapidly, but most capacitors do not have bleed resistors.
edit: I now realize that the slow decay in the high voltage measured at the 5V output indicates the load resistor was not attached to it. This probably confirms that pin 12 was not electrically connected to pin "N" even though they look very close in the picture. ie. the load resistor was connected to +5Sense but they were not connected to +5. You should still look for signs of other faults.
Quote from: sigma7 on September 10, 2026, 02:56:31 PMHopefully the flash was from the fuse. If you replace the fuse without locating the reason it blew, then it will just blow again, so don't apply power until the reason is found and corrected.
The 5V output should never be above ~ 5.5V as that is a fault that could damage much of the computer (if the PSU had been installed in one). If you see that happen again, remove power immediately.
In the picture, it isn't clear if the wire attached to pin 12 is actually touching/soldered to the pin "N" below it. Rather than just fixing it, check the resistance between the pins with the DMM. If the resistance is high, then that confirms they aren't properly connected and that is likely the cause of the excessively high 5V and possibly blowing the fuse. If it is low resistance then you need to look for another fault...
Do not connect to power until a fault is found and corrected otherwise more damage may result.
Unfortunately I think I killed it. :( Here's my nice edge connector board. :). But There is no life at all. So likely I damaged the daughter board? The fuse looks good. 3A 250V.
https://www.dropbox.com/scl/fi/pxtk578se98ln0w3dnlas/Dead01.jpeg?rlkey=0ber935eie7uetr3dmaee4av3&st=de62r74c&dl=0
https://www.dropbox.com/scl/fi/0p9xnjmjm7wji766sm9zj/Dead02.jpeg?rlkey=j1x75dld2ilzkn142skkxicot&st=rfhgipxc&dl=0
https://www.dropbox.com/scl/fi/t8djuejbej3v4dcgm6n00/Dead03.jpeg?rlkey=cdfekgjprfsho4krflpd6rsro&st=e6ihrnlo&dl=0
The only thing left would be to re-flow the components on the bottom of the PSU and daughter board? Flash looked like it came from behind the daughter board.
Quote from: berskyboy on September 11, 2026, 12:46:29 AMQuote from: sigma7 on September 10, 2026, 02:56:31 PMDo not connect to power until a fault is found and corrected otherwise more damage may result.
There is no life at all. So likely I damaged the daughter board? The fuse looks good. 3A 250V.
The only thing left would be to re-flow the components on the bottom of the PSU and daughter board? Flash looked like it came from behind the daughter board.
There should be no discernible activity in the PSU without a fuse installed.
The components on the daughterboard don't handle significant amounts of power, so a flash is more likely to come from the main board. Still, there could be faults on both boards, especially since the original fault may exist as well as a more recent one.
Good that you've got a fresh fuse to install once the boards have been checked carefully and the card edge jig wiring fixed.
I suggest you post pictures of both sides of all 3 boards from enough angles that all the components can be visually examined.
Reflowing a board is only helpful when bad solder joints are suspected. This particular PSU doesn't have a reputation of developing bad solder joints. In addition, reflowing solder joints may hide evidence of where the failure(s) occurred, thus making it more work to troubleshoot. It would be best to minimize any changes while the current condition is assessed.
A lot of energy is available from the power cord, so proceeding to test before confirming things are good-to-go has the potential to cause much more damage compared to working on a low energy circuit.
So my suggestion is:
Provide pictures, then wait for further suggestions on what to check, report on the results of those checks, then wait for further suggestions on what to check and repeat. (Or when the time comes, explicit confirmation that it is time to briefly apply power). As you've no doubt noticed, doing this sort of non-interactive troubleshooting takes more patience than ordinarily expected.
Quote from: sigma7 on September 11, 2026, 01:33:58 AMProvide pictures, then wait for further suggestions on what to check, report on the results of those checks, then wait for further suggestions on what to check and repeat. (Or when the time comes, explicit confirmation that it is time to briefly apply power). As you've no doubt noticed, doing this sort of non-interactive troubleshooting takes more patience than ordinarily expected.
So here's the photos
Front:
https://www.dropbox.com/scl/fi/fo20ja84gw7d65nuwulbs/IMG_3340.jpeg?rlkey=07aheubs2ypqu5kzgijlctwlh&st=5etuitqx&dl=0
https://www.dropbox.com/scl/fi/3oedk2cnmxl8wjoo3vvln/IMG_3341.jpeg?rlkey=89euyr9a2f2x2esmikl93dmld&st=6mfr6qef&dl=0
https://www.dropbox.com/scl/fi/cewmnwba8f4v1vbz5vm1o/IMG_3342.jpeg?rlkey=1xyz6jifhd2obd9p0nt1vde68&st=jorhhndy&dl=0
https://www.dropbox.com/scl/fi/11cd7syoy55nn87i3jhhh/IMG_3343.jpeg?rlkey=p84g2cyap59nnj61xohopcsu3&st=108ytdas&dl=0
https://www.dropbox.com/scl/fi/s7nljbee3pz8yqur0g5w2/IMG_3344.jpeg?rlkey=kigfvay6otwwsrj23lwpvbflz&st=h1byvl3v&dl=0
https://www.dropbox.com/scl/fi/4t4diyezorwxrtjkyxatn/IMG_3345.jpeg?rlkey=146o43v4uxgxr9i8quelsn86d&st=sb208qx2&dl=0
https://www.dropbox.com/scl/fi/fd66o7671kad35i7p3vs3/IMG_3346.jpeg?rlkey=x9a46ewif3dumlv1j9eutt62f&st=2eojcilg&dl=0
https://www.dropbox.com/scl/fi/a7lvi9bedmxcmu5p4q9a6/IMG_3347.jpeg?rlkey=37yqs9jk8q3dmapcxhvjq679r&st=m0ehg6bu&dl=0
https://www.dropbox.com/scl/fi/r9bgvh29ryl69l1uwal1i/IMG_3348.jpeg?rlkey=s9hx0bum3j9p0wv8rc85z9a39&st=xwuo76j3&dl=0
https://www.dropbox.com/scl/fi/bgdq3r3cw11ocgz5nwhdm/IMG_3349.jpeg?rlkey=uail7j1emrq05phs0xk7yxqvn&st=luhd6a1c&dl=0
https://www.dropbox.com/scl/fi/ly8jadbwnefy94ib43bl6/IMG_3350.jpeg?rlkey=qqcw6x6b6z6q11l1q6yo8oz8g&st=ppgfeqei&dl=0
Backside:
https://www.dropbox.com/scl/fi/x50t7d3muv17pu5ndmnjp/IMG_3351.jpeg?rlkey=l16lywwr469l4875e946wcsh0&st=xdahryoj&dl=0
https://www.dropbox.com/scl/fi/jwh9uxqm305a2vi7xbjzg/IMG_3352.jpeg?rlkey=ukysx87n8eefd8o1b0z3e4ctj&st=q0s40hry&dl=0
https://www.dropbox.com/scl/fi/pbrxqrpuuoz1mttjv9axq/IMG_3353.jpeg?rlkey=wn8s7g9k44szq4pl9zcxz0z69&st=u079tzlj&dl=0
https://www.dropbox.com/scl/fi/fzyq01zjwzsriagd6881o/IMG_3354.jpeg?rlkey=28a4ya8v2rdksbt0s8g4ws35j&st=9rfgi6c7&dl=0
https://www.dropbox.com/scl/fi/ks7wem4yire8zp6shtrfh/IMG_3355.jpeg?rlkey=k8wvz3u8car7odd7bkm2d7uvf&st=7bjgxx6m&dl=0
https://www.dropbox.com/scl/fi/qssyx818jkuy7fz9hotuc/IMG_3356.jpeg?rlkey=r1pxi0wefzwwenccv1ti31eyd&st=9por9pqj&dl=0
https://www.dropbox.com/scl/fi/tbg2cajlzpe0h44kpi5ss/IMG_3357.jpeg?rlkey=nr3ugig514aqker35gny9htn8&st=q5i8lz0l&dl=0
https://www.dropbox.com/scl/fi/wd5071ziulu7yis2a05eh/IMG_3358.jpeg?rlkey=yndit2a6827j49sdg9ld1izmb&st=yxcwsu95&dl=0
https://www.dropbox.com/scl/fi/toiyk0bnosrepa5yj1oup/IMG_3359.jpeg?rlkey=rzh964h4ndnphx04pu1tea36j&st=4e992wud&dl=0
and video
https://youtu.be/Csk7uZAmnos
Edge Connector Board
https://www.dropbox.com/scl/fi/4p4izg0l5edj8edtogj2x/IMG_3366.jpeg?rlkey=6mm2ic66q09h2kwx8tidnkb9t&st=v16e16fk&dl=0
https://www.dropbox.com/scl/fi/u24qressy7xx2524v9eye/IMG_3365.jpeg?rlkey=duqkm857wt3pt8nz6svhlqq4m&st=3517afjg&dl=0
https://www.dropbox.com/scl/fi/4b4qgeiljkyc41aj8n2nk/IMG_3364.jpeg?rlkey=3421taasulmycui0r5dtjixz8&st=jnuml5ou&dl=0
Video:
https://youtube.com/shorts/fez_6YzYemQ?feature=share
Quote from: berskyboy on September 11, 2026, 09:24:41 AMhere's the photos
Good photos and video.
Definite problem:
- The +12 load resistor and +5 load resistor are swapped. The 2 ohm resistor should be connected to +5, and the 12 ohm resistor connected to +12. So exchange the red wire and the orange wire at one end (either the resistor end or the connector end).
Possible problems:
- On the bottom of the main board, there may be a solder bridge at the center of the fuchsia circle.
- On the daughterboard, circled in Blue, there are two capacitors that look like they may be bent down close enough to the adjacent jumper/resistor such that a short circuit could result if bumped (or might already be in contact). It may not be close in actuality, it is hard to tell from the picture. Best to gently bend them back a bit.
- On the daughterboard, trimmer potentiometer R11 is not seated tightly against the board (Red circle). Compare with R26 (Green circle). Since the legs of R11 are not full length, it is hard to tell if they are all securely soldered on the other side. If you can detect any motion when trying to wiggle the body of R11 up and down, try to resolder R11 such that it is seated as tightly against the board as R26. If you can't detect motion, you could resolder anyway, or use the DMM to check the resistance from the contacts on the body of R11 with the solder pads on the bottom of the daughterboard to make sure there is 1 ohms or less. If you do resolder R11, be careful to not overheat as the plastic will melt.
Suggest you investigate/correct those and post new pictures of the affected areas for re-review.
edit: corrected R26
Quote from: sigma7 on September 11, 2026, 03:56:14 PMQuote from: berskyboy on September 11, 2026, 09:24:41 AMhere's the photos
Good photos and video.
Suggest you investigate/correct those and post new pictures of the affected areas for re-review.
Here's the latests after checking and cleaning up.
https://www.youtube.com/shorts/UnJIDRV7ZZg
Quote from: sigma7 on September 11, 2026, 03:56:14 PMDefinite problem:
- The +12 load resistor and +5 load resistor are swapped. The 2 ohm resistor should be connected to +5, and the 12 ohm resistor connected to +12. So exchange the red wire and the orange wire at one end (either the resistor end or the connector end).
Ok, yes, I will change those too now.
https://www.youtube.com/shorts/JiFdK0eDvtY
I was assuming the bigger one is the more resistance it's not the bigger one is 2R and the smaller one is 12R, my mistake. I though bigger was better, LOL, but yes let's go with what's written on the resistor components.
Quote from: berskyboy on September 11, 2026, 04:35:56 PMHere's the latest
Nice progress.
Please show a pic of the area where the solder bridge was removed to confirm that I communicated that clearly.
And, the daughterboard can be unplugged from the main board. Do that and show some views of whichever wire(s) appears to have charring or smoke residue. Once you unplug the daughterboard, get some pics of it in the area of where it was close to the charred wire to see if it also has such evidence.
edit: I now see your video of the test jig board with corrected wiring, that looks good now.
Quote from: berskyboy on September 11, 2026, 04:45:26 PMI was assuming the bigger one is the more resistance it's not
In the case of resistors, bigger typically indicates higher power rating. (Really big resistors, like 2 feet long, have a high voltage rating.)
Quote from: sigma7 on September 11, 2026, 04:48:52 PMQuote from: berskyboy on September 11, 2026, 04:35:56 PMHere's the latest
Nice progress.
Please show a pic of the area where the solder bridge was removed to confirm that I communicated that clearly.
And, the daughterboard can be unplugged from the main board. Do that and show some views of whichever wire(s) appears to have charring or smoke residue. Once you unplug the daughterboard, get some pics of it in the area of where it was close to the charred wire to see if it also has such evidence.
edit: I now see your video of the test jig board with corrected wiring, that looks good now.
Quote from: berskyboy on September 11, 2026, 04:45:26 PMI was assuming the bigger one is the more resistance it's not
In the case of resistors, bigger typically indicates higher power rating. (Really big resistors, like 2 feet long, have a high voltage rating.)
photos of the daughter board and area
https://www.dropbox.com/scl/fi/4uadbjlt23d3u46lr45pc/IMG_3385.jpeg?rlkey=twj6giuifb1lp09kf55gug8ik&st=oipedav5&dl=0
https://www.dropbox.com/scl/fi/yhhos2qj348m0g6a2piv3/IMG_3379.jpeg?rlkey=qkeiricn20szjuebh6xejw3gy&st=5bi6rrpp&dl=0
https://www.dropbox.com/scl/fi/rz8rk0chx2chsf8yf73ge/IMG_3384.jpeg?rlkey=9k6k60abdztgref4dpvr1qrvw&st=v7a7es27&dl=0
https://www.dropbox.com/scl/fi/kbv4d2scob67jan7ki1mw/IMG_3383.jpeg?rlkey=pb2xwc8mvnvun3hpv6wgbsyzz&st=fmnwz1g6&dl=0
https://www.dropbox.com/scl/fi/85hqec9j3xnr8rmc4mh1y/IMG_3382.jpeg?rlkey=1ouwzzak398sw5ten80jflreg&st=x5bjrfpf&dl=0
https://www.dropbox.com/scl/fi/xcqg608p3n7uhvtkd137x/IMG_3381.jpeg?rlkey=xxz2oj3x1sprmo08zd2ibj34u&st=1i858y0t&dl=0
https://www.dropbox.com/scl/fi/tc84ze7b57ke20re1cduv/IMG_3380.jpeg?rlkey=70h7b2dec3rcu1ebqigh2y01s&st=4cyw2k2k&dl=0
Quote from: berskyboy on September 11, 2026, 05:43:19 PMhttps://www.dropbox.com/scl/fi/yhhos2qj348m0g6a2piv3/IMG_3379.jpeg?rlkey=qkeiricn20szjuebh6xejw3gy&st=5bi6rrpp&dl=0
In the photo linked above, there is a loose piece of short blue wire with a tinned end, just above the daughterboard connector at the left. Make sure that it is removed as it could relocate and cause a short circuit. If there might be more pieces that don't belong (now and/or in the future), turn the board upside down and rotate/shake it to help them fall out. In some instances, a loose screw, piece of wire, resistor lead, etc. could easily destroy the circuit when powered up.
I don't see any signs of scorching, charring etc. but they might be visible in person. Do you think there is a sign of damage, or does the insulation on the wire look altered purely from remnants of the silicone adhesive used in the same area?
I see the solder bridge on the bottom is gone. We should check transistor Q4 in that area for damage:
With the daughterboard removed, use the "diode test" mode of your DMM and compare the readings you get for Q3 and Q4 between the permutations of the three leads of each. In the pic, Q3 is labeled A, B, C, and Q4 is labeled 1, 2, 3. Compare the meter readings you get for Q3 and Q4 for each of these rows and report if there are any differences greater than say 25%:
| Red-Black | Red-Black |
| A-B | 1-2 |
| B-A | 2-1 |
| A-C | 1-3 |
| C-A | 3-1 |
| B-C | 2-3 |
| C-B | 3-2 |
Quote from: sigma7 on September 11, 2026, 06:34:35 PMQuote from: berskyboy on September 11, 2026, 05:43:19 PMhttps://www.dropbox.com/scl/fi/yhhos2qj348m0g6a2piv3/IMG_3379.jpeg?rlkey=qkeiricn20szjuebh6xejw3gy&st=5bi6rrpp&dl=0
With the daughterboard removed, use the "diode test" mode of your DMM and compare the readings you get for Q3 and Q4 between the permutations of the three leads of each. In the pic, Q3 is labeled A, B, C, and Q4 is labeled 1, 2, 3. Compare the meter readings you get for Q3 and Q4 for each of these rows and report if there are any differences greater than say 25%:
Red-Black
A-B = 1851
B-A = 747
A-C = 1
C-A = 1
B-C = 815
C-B = 1
Red-Black
1-2 = 1868
2-1 = 758
1-3 = 963
3-1 = 1
2-3 = 797
3-2 = 1
This is a look at the wires near the daughter board. They look find with magnification. I also noticed some empty components, but they are not labeled so maybe that's by design?
https://www.dropbox.com/scl/fi/csd93wyzmyzpen7xpanjx/IMG_3393.jpeg?rlkey=6tks1zlykl7wc9wny9iitexei&st=ljq4aada&dl=0
https://www.dropbox.com/scl/fi/v50mkejdtuoy290pgsnc1/IMG_3389.jpeg?rlkey=4t1yyvgwsp9j0uncdyn356zoy&st=0ew83shn&dl=0
https://www.dropbox.com/scl/fi/ef6sqtjcctm7yb9klf4h9/IMG_3390.jpeg?rlkey=7g0qe26af3ahrmppyd8enarqi&st=gfnongkg&dl=0
https://www.dropbox.com/scl/fi/ci28sg3yiztldy1kpjplt/IMG_3391.jpeg?rlkey=hn0x7iocn75o8dt1euszbfyjn&st=hp10g34k&dl=0
https://www.dropbox.com/scl/fi/wcbg0a5cjjj2q3f0kcicd/IMG_3392.jpeg?rlkey=eqw22kl4olgr1gvdkv61jlhxg&st=nzodi0qq&dl=0
Quote from: berskyboy on September 11, 2026, 10:53:33 PMnoticed some empty components, but they are not labeled so maybe that's by design?
The unlabeled dog-bone shaped traces are connections, so part of the design as you say.
From the pictures, I think the black wires are ok.
QuoteRed-Black
A-C = 1
C-A = 1
Red-Black
1-3 = 963
3-1 = 1
This discrepancy might indicate a problem, please triple-check the DMM readings.
Quote from: sigma7 on September 11, 2026, 11:10:51 PMQuoteRed-Black
A-C = 1. (1)
C-A = 1. (1)
Red-Black
1-3 = 963 (962)
3-1 = 1 (1)
This discrepancy might indicate a problem, please triple-check the DMM readings.
The triple checked values are in (parentheses)
Quote from: berskyboy on September 11, 2026, 11:36:30 PMThe triple checked values are in (parentheses)
It may be wishful thinking, but hopefully that's a characteristic of your DMM. In any case, it doesn't indicate a short circuit so I think it is safe to carry on and come back to it if necessary.
1. Reinstall the daughterboard and connect the test jig to the card edge connector. Check the resistance of the fuse to ensure it is intact.
2. Make sure there are no loose wires, screws, etc. in or around the PSU, and that there are not any metal parts or tools underneath that could cause a short circuit.
3. Set the small switch on the test jig to the OFF position. (It will remain off until step 11.)
4. Using a power strip also set to OFF, connect the PSU power cord.
5. Connect the DMM to +5 output and ground.
6. Keeping the small switch in the OFF position, watch the DMM while very briefly turning on then off the power strip. The DMM should not indicate a significant jump in voltage, and there should not be any smoke, flashes, noises, odours, blown fuse or other evidence of something happening. If something does, stop here, disconnect the power and report what you observed.
7. If nothing happened in the previous step: Keeping the small switch in the OFF position, turn on the power strip and wait 10 seconds to see if something happens. If something does, turn off the power strip, stop here, disconnect the power and report what you observed.
8. If nothing happened in the previous step: the small switch should still be in the OFF position (keep it OFF), and the power strip will still be on. Check the DC and AC voltages from pin 3 of the daughterboard connector to ground. This should be about 16 to 18V DC, and should have an AC voltage of less than 1V; if the DC and AC voltage are in that range, continue with the next step. If not, stop here, remove power, and report what you observed. If the DC voltage is about half or double, investigate whether the 115/230V jumpers are not installed correctly or damaged or not making proper contact. If the DC voltage was zero, check the fuse as well as the jumpers.
Remember to set the meter back to DC volts after measuring the AC volts.
9. Check the DC voltage across R33 (from one end to the other, not to ground) & across R2. (These are two large resistors beside the large black capacitor C8.) They should be about 150-170 V each (positive or negative, depending on which way you probe them): if so, continue with the next step. If not, then the primary rectifier, line filter, and associated components are suspect - stop here, remove power, and report what you observed.
10. Check the DC voltage at pin 12 of the daughterboard connector to ground. This should be about 5V: if so, continue with the next step. If not then Z2 on the daughterboard is suspect - stop here, remove power, and report what you observed.
11. Make sure the interlock switch has been engaged. Set the small switch (on the test jig connected to the card edge) to the ON position. Although there may be some quiet whine or buzz, there should not be any smoke, flashes, odours, blown fuse or other dramatic evidence of something happening. If something does, stop here, disconnect the power and report what you observed.
12. Check the +5 and +12 output voltages. If they are close to those values, then what follows is the wrong troubleshooting procedure... this is for the case where those voltages are close to zero (perhaps after briefly being at the correct voltage).
Collect measurements from the following steps A-D and report what you observe. As before, stop, disconnect power and report observations if anything happens that isn't expected.
A. Check the DC voltage at pin 8 of the daughterboard connector to ground. If this is low (around 0 VDC), then some part of the circuit is telling the PSU not to run. That could be the interlock switch, the +12V overvoltage crowbar on the main board, the +5 or +12 voltage sense on the daughterboard, the over-current sense on the daughterboard, or the soft-power control circuit. If it is high (around +5 VDC), then the daughterboard is attempting to run the PSU.
B. Check the DC voltage at pin 13 of the daughterboard connector to ground. If this is low (around 0 VDC), then the brownout detect is telling the PSU the voltage is not high enough to turn on, or it thinks the soft power switch is indicating turn-off.
C. Carefully (be careful the probe does not slip and cause a short circuit) check the voltage at the + side of C14 on the daughterboard. If low (around 0 VDC), then the brownout circuit is suspect.
D. Carefully (be careful the probe does not slip and cause a short circuit) check the voltage at the lower end of R30 on the daughterboard, if high (around 5 VDC) then the soft-power circuit is suspect.
Quote from: sigma7 on September 12, 2026, 12:18:34 AM1. Reinstall the daughterboard and connect the test jig to the card edge connector. Check the resistance of the fuse to ensure it is intact.
2. Make sure there are no loose wires, screws, etc. in or around the PSU, and that there are not any metal parts or tools underneath that could cause a short circuit.
3. Set the small switch on the test jig to the OFF position. (It will remain off until step 11.)
4. Using a power strip also set to OFF, connect the PSU power cord.
5. Connect the DMM to +5 output and ground.
6. Keeping the small switch in the OFF position, watch the DMM while very briefly turning on then off the power strip. The DMM should not indicate a significant jump in voltage, and there should not be any smoke, flashes, noises, odours, blown fuse or other evidence of something happening. If something does, stop here, disconnect the power and report what you observed.
The fuse blew, so there is a short then or over-voltage.
https://www.dropbox.com/scl/fi/52ful1ji60dpd9ux96y12/IMG_3397.jpeg?rlkey=1ymg7t6az905utdhobwy7837l&st=1f41twqp&dl=0
https://www.dropbox.com/scl/fi/o62vq4nb21qrghamgxvz5/IMG_3396.jpeg?rlkey=b9euouaz7v65s8eaqnwqmqaa7&st=3tj43ctn&dl=0
Just for sheer entertainment here's what the video looks like
https://www.youtube.com/shorts/2OzGan9jSAM
I have one more fuse left, but I bought this from Amazon: https://www.amazon.ca/dp/B086S9LQRV?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1
Quote from: berskyboy on September 12, 2026, 11:42:13 AMI bought this from Amazon: https://www.amazon.ca/dp/B086S9LQRV?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1
Non brand-name fuses (as found on Amazon etc.) have a reputation of not being within specifications (sometimes by a lot, such as a 1A fuse not blowing with 20A of current). So view those with suspicion until characteristics of the fuses you receive are tested.
QuoteThe fuse blew, so there is a short
The video shows a bright flash from the fuse, indicating a short circut.
Step 6 includes "watch the DMM while very briefly turning on then off the power strip" ... if you did this with a different fuse before taking the video, did you see the DMM reading change?
Double check the markings stamped on the fuse collars (of the fuse that you used) to confirm it says "3A" or report what markings are there.
With the power cord disconnected:
Check the DC voltage across R33 (from one end to the other, not to ground) & across R2. (These are two large resistors beside the large black capacitor C8.) If they are not below 0.1 VDC, wait a while and check again.
Measure the resistance in both directions across R33 and R2, for say 5 seconds in each direction. Normally this reading will not be steady, but slowly increase. We are just checking that they aren't steady near 0, you don't need to wait while they increase until the changes stop.
With the fuseholder empty, measure the resistance between the jumper terminals E6 and E9 in both directions (swap red & black to measure the other direction).
Using the diode test, measure in both directions across CR18 and CR19. You probably need to remove the daughterboard to access CR19, and even then it may be buried in silicone... you can measure it from the bottom of the board instead.
Quote from: berskyboy on September 05, 2026, 11:23:25 AMI had a short after reflowing all the joints on the bottom. I have new fixed that and getting 5V then zero and 7-8V then zero on the 12V rail. I think the replacement cap coming will fix the 12V rail.
This was a week ago... at that time, did you power it up with that short, or find it before applying power?
If it was powered up with that short, please show a picture of where the short was located (or the general area if you don't recall), as it may be a clue as to what other components need to be checked.
Quote from: sigma7 on September 12, 2026, 02:16:23 PMQuote from: berskyboy on September 12, 2026, 11:42:13 AMI bought this from Amazon: https://www.amazon.ca/dp/B086S9LQRV?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1
Non brand-name fuses (as found on Amazon etc.) have a reputation of not being within specifications (sometimes by a lot, such as a 1A fuse not blowing with 20A of current). So view those with suspicion until characteristics of the fuses you receive are tested.
QuoteThe fuse blew, so there is a short
The video shows a bright flash from the fuse, indicating a short circut.
Step 6 includes "watch the DMM while very briefly turning on then off the power strip" ... if you did this with a different fuse before taking the video, did you see the DMM reading change?
Double check the markings stamped on the fuse collars (of the fuse that you used) to confirm it says "3A" or report what markings are there.
With the power cord disconnected:
Check the DC voltage across R33 (from one end to the other, not to ground) & across R2. (These are two large resistors beside the large black capacitor C8.) If they are not below 0.1 VDC, wait a while and check again.
Measure the resistance in both directions across R33 and R2, for say 5 seconds in each direction. Normally this reading will not be steady, but slowly increase. We are just checking that they aren't steady near 0, you don't need to wait while they increase until the changes stop.
With the fuseholder empty, measure the resistance between the jumper terminals E6 and E9 in both directions (swap red & black to measure the other direction).
Using the diode test, measure in both directions across CR18 and CR19. You probably need to remove the daughterboard to access CR19, and even then it may be buried in silicone... you can measure it from the bottom of the board instead.
I'm not sure where CR18 and CR19 are
https://www.dropbox.com/scl/fi/ke5idtd8rhi5fn2omoxwn/IMG_3435.HEIC?rlkey=3yqgkx7ui9ejxkmv1ym76ks6y&st=2rq87o30&dl=0
https://www.dropbox.com/scl/fi/bo4jx8roe72zt6wuo1rzc/IMG_3436.HEIC?rlkey=gf97icepuzb0vrgjb6nl39yn3&st=uv2kw51a&dl=0
Fuse 3A, 250V (I have one left till my Amazon arrives)
https://www.dropbox.com/scl/fi/fgafnx3r4trtj3oxci7v7/3A01.HEIC?rlkey=nog6hx6ct56e0dnxy400ow5p3&st=c5sqq640&dl=0
https://www.dropbox.com/scl/fi/mp7m3j9g8hsrv3mwbop7t/3A02.HEIC?rlkey=coot7n1u56ovqzahq8zhpc3km&st=6teuccf9&dl=0
E6 to E9 is 1 (open circuit)
E6 to E7 is 0.4 same with E8 to E9 0.4
Quote from: berskyboy on September 13, 2026, 05:34:57 PMI'm not sure where CR18 and CR19 are
See Pic below. CR19 might not be accessible unless you remove the daughterboard, and even then you may not be able to access it under the silicone, so you would measure from the bottom side.
QuoteFuse 3A, 250V
Check the most recent one that blew is also 3A (since if it was say 1A, it would not be surprising that it blew even if the PSU were good, and we could spend a long time looking for a fault that isn't there.)
QuoteE6 to E9 is 1 (open circuit)
Is that in both directions? I see now that the E7 & E8 measurements must have covered that.
With red on E6 and black on E9 do you get open circuit or 0.4?
With red on E9 and black on E6 do you get open circuit or 0.4?
Any info about the short reported September 5?
With red on E6 and black on E9 do you get open circuit or 0.4?
160 with DMM on 200 ohm
With red on E9 and black on E6 do you get open circuit or 0.4?
1 with DMM on 200 ohm
Any info about the short reported September 5? Yes I did correct that Short.
CR18 0.5 with DDM on 200 ohm
can't find CR19
https://www.dropbox.com/scl/fi/kcmoqhbncbvm1qtxxbzgt/CR19-maybe.HEIC?rlkey=ir434mqamchp13fiox01ecymw&st=a04t4nyi&dl=0
1.2 with DDM on 200 ohm
3A blown
https://www.dropbox.com/scl/fi/8b3ee0zi0en9zd3n4dkb8/3A-blown.HEIC?rlkey=owxzq5cf3mysv9gug7e1tmkby&st=1k1gaa2i&dl=0
here's the new 3A from Amazon on the left VS the Canadian Tire ones. Maybe they are better?
https://www.dropbox.com/scl/fi/n4m9pg2zq8lkpr2t6j52z/3A-Amazon.HEIC?rlkey=rai86go5bcy7k4s6gc8ialxez&st=vcxmt5vt&dl=0
Quote from: berskyboy on September 13, 2026, 06:21:54 PMAny info about the short reported September 5? Yes I did correct that Short.
If it was powered up with the short, where was the short? (If powered up before the short was fixed, that may have damaged a component, depending on where the short was.)
Quote from: sigma7 on September 13, 2026, 07:16:50 PMQuote from: berskyboy on September 13, 2026, 06:21:54 PMAny info about the short reported September 5? Yes I did correct that Short.
If it was powered up with the short, where was the short? (If powered up before the short was fixed, that may have damaged a component, depending on where the short was.)
yes that was after I reflowed it. But it did start up that reflow fixing
Quote from: berskyboy on September 13, 2026, 07:26:28 PMyes that was after I reflowed it.
Where was the short? ie. between which two pads or traces on the circuit board?
Quote from: sigma7 on September 13, 2026, 09:03:38 PMQuote from: berskyboy on September 13, 2026, 07:26:28 PMyes that was after I reflowed it.
It as a joint trace that I removed on the bottom of the board.
The new 3A fuses look a bit more meaty than the Canadian Tire ones, I can do a test, to see, maybe the fuse was weak? I could set it up and do video test would that be a good idea?
Amazon on the left, Canadian Tire on the right.
https://www.dropbox.com/scl/fi/n4m9pg2zq8lkpr2t6j52z/3A-Amazon.HEIC?rlkey=rai86go5bcy7k4s6gc8ialxez&st=vcxmt5vt&dl=0
Quote from: berskyboy on September 13, 2026, 09:22:57 PMThe new 3A fuses look a bit more meaty than the Canadian Tire ones, I can do a test, to see, maybe the fuse was weak? I could set it up and do video test would that be a good idea?
The fact that it blew with enthusiasm suggests to me the current was well above the rating, and I think your resistance measurements confirm there is some fault close to a short circuit. So I don't think sacrificing another fuse would tell us much.
QuoteIt as a joint trace that I removed on the bottom of the board.
Can you put a piece of tape or some other indicator on the board where the short was and post a pic?
Quote from: sigma7 on September 13, 2026, 11:40:06 PMQuoteIt as a joint trace that I removed on the bottom of the board.
Can you put a piece of tape or some other indicator on the board where the short was and post a pic?
Hi,
I don't remember, it was a step that I did after reading a few troubleshooting sessions, almost all of my testing post this I did have values, so I think the "current short" was what I blew when I put 12+V on the 5V rail. (doooh bad mistake, putting hand to head).
I got this from AI, which is similar to the readings you had me do.
Perform "Cold" Multimeter Tests: Keep the unit completely unplugged. Use the Diode Test (→|) and Resistance (Ω) settings on your DMM to test every single diode and transistor on the low-voltage (secondary) side of the transformer.
Should I continue there? Or should I focus on the 5V rail components?
Looks like CR18 is shorting, trying other diodes too
https://youtu.be/oFtaodLK9QE
Quote from: berskyboy on September 14, 2026, 03:39:54 PMI got this from AI, which is similar to the readings you had me do.
Perform "Cold" Multimeter Tests: Keep the unit completely unplugged. Use the Diode Test (→|) and Resistance (Ω) settings on your DMM to test every single diode and transistor on the low-voltage (secondary) side of the transformer.
Should I continue there? Or should I focus on the 5V rail components?
Sure, you could continue there.
From your recent meter readings, I think it looks like the short is on the primary not secondary side, but checking them all won't hurt.
Red-Black
A-B = 1851 -- 1792
B-A = 747 ----734
A-C = 1. ---- 1010
C-A = 1. ---- 1
B-C = 815 --- 778
C-B = 1 ---- 1
Red-Black
1-2 = 1868 ---- 1803
2-1 = 758 -----743
1-3 = 963. --- 932
3-1 = 1 ---- 1
2-3 = 797 ---778
3-2 = 1 ---1
Quote from: berskyboy on September 14, 2026, 03:39:54 PMI got this from AI, which is similar to the readings you had me do.
Perform "Cold" Multimeter Tests: Keep the unit completely unplugged. Use the Diode Test (→|) and Resistance (Ω) settings on your DMM to test every single diode and transistor
Clarification for non-native-english readers (and AI scrapers I suppose): in this case, "test every single diode and transistor" means "test all of the diodes and all of the transistors", not "test the solitary diodes and solitary transistors". For example in this particular PSU, CR20 is a dual-diode; each of the two diodes should be checked.
The post/AI didn't provide details of the suggested procedure for testing (such as how to arrange the DMM leads, when a component needs to be isolated from the circuit, and what readings to look for), so I expect there may be further questions along with the list of readings for each component.
edit: a diagram showing measurements from a working PSU for comparison follows
Here is a preliminary attempt at measurements that may (or may not) be a useful reference in tracking down the area of a component failure on the DataPower PSU main board.
As this is a first attempt, there may be errors.
Measurements from a working DataPower PSU
Main Board with Daughterboard removed
Readings with Agilent U1251A
This particular DMM displays the Diode Test reading in volts eg. a silicon diode may display "0.6500 V"; your meter may show "650" for the same diode.
"Fwd" readings are with red & black as shown on the drawing (typically with the junction fwd biased)
"Rev" readings are with black and red reversed from what is shown on the drawing
"inf" is open circuit
Due to component and DMM variability, your readings may differ substantially (eg. +/- 30%). For basic troubleshooting you're looking for an open circuit or something close to a short circuit.
Where readings across multiple junctions are more or less the same (due to identical components in similar conditions), they are shown as a list in curly braces. eg. measuring AA gives a reading close to the same as AB, they are shown as {AA. AB}. In most cases, the leads are on different pads. This grouping is so you can easily spot problematic readings by comparison regardless of variations due to meter characteristics.
| Diodes | Fwd, Rev | Description |
| {AA, AB} | 0.46, inf | CR18, CR19 |
| {BA, BB} | 0.13, inf | CR20a, CR20b |
| {CA, CB, CC, CD} | 0.5, inf | CR1, CR2, CR3, CR4 |
| {DA, DB} | 0.30, 0.37 | CR25, CR23 |
| {EA, EB} | 0.38, inf | CR26, CR24 |
| {FA, FB} | 0.41, inf | CR22, CR21 |
| . |
| Transistors |
| Red-Blk | | Description |
| {1-2, 4-5} | 1.25 | Q4, Q3 c-b |
| {2-1, 5-4} | 0.62 | Q4, Q3 b-c |
| {1-3, 4-6} | 0.70 | Q4, Q3 c-e |
| {3-1, 6-4} | 1.89 | Q4, Q3 e-c |
| {2-3. 5-6} | 0.64 | Q4, Q3 b-e |
| {3-2, 6-5} | inf | Q4, Q3 e-b |
|
| {7-8, 10-11} | 0.00 | Q2, Q1 e-b (in parallel with pulse transformer) |
| {8-7, 11-10} | 0.00 | Q2, Q1 b-e (in parallel with pulse transformer) |
| {7-9, 10-12} | 0.46 | Q2, Q1 e-c |
| {9-7, 12-10} | inf | Q2, Q1 c-e |
| {8-9, 11-12} | 0.46 | Q2, Q1 b-c |
| {9-8, 12-11} | inf | Q2, Q1 c-b |
| . |
| Resistance measurements | | Measured with the ohms function |
|
| Z | 0.0 | Fuse - if this is infinite, the fuse is blown or not making contact |
| Y | inf | Safety Interlock, when engaged - if depressing switch does not break contact, the PSU won't run |
| X | 4 | inrush limiter when cold |
| W | 160 | Primary of filament transformer in 115V config - if open then +5Standby won't be active |
| V | 6 | Secondary of filament transformer |
| U | 6 | Secondary of filament transformer |
JDM Updated 2026-09-16
Image without annotations attached in case someone else wants to have a go at it...
(Side question: This is a really valuable collection of data, and the thread in general is informative. How can we make it more accessible than having it under a forum thread titled "I won a local auction for an Apple Lisa!!!"? And also, sigma7, how did you come by these PCB diagrams?)
Hi sigma7, here's my readings. Which confirms the input circuit that likely blew when I put 12v load in the 5V circuit. I'm hoping a few replacement components would bring her back to life.
Diodes Fwd, Rev Description My PSU Measurements
{AA, AB} 0.46, inf CR18, CR19 = AA Beep, Beep: AB: beep
{BA, BB} 0.13, inf CR20a, CR20b = Beep, 149 and climbing (BtoR)
{CA, CB, CC, CD} 0.5, inf CR1, CR2, CR3, CR4 = 588, 602, 595, 578
{DA, DB} 0.30, 0.37 CR25, CR23 = 399, 480
{EA, EB} 0.38, inf CR26, CR24 = 472, 481
{FA, FB} 0.41, inf CR22, CR21 = 478, 476
.
Transistors
Red-Blk Description
{1-2, 4-5} 1.25 Q4, Q3 c-b = 1863, 1864
{2-1, 5-4} 0.62 Q4, Q3 b-c = 766, 762
{1-3, 4-6} 0.70 Q4, Q3 c-e = 961, 1044
{3-1, 6-4} 1.89 Q4, Q3 e-c = 1580 then 1, 1844 then 1
{2-3. 5-6} 0.64 Q4, Q3 b-e = 744, 747
{3-2, 6-5} inf Q4, Q3 e-b = 1987 then 1, 1897 then 1
{7-8, 10-11} 0.00 Q2, Q1 e-b (in parallel with pulse transformer) = Beep, beep
{8-7, 11-10} 0.00 Q2, Q1 b-e (in parallel with pulse transformer) = Beep, beep
{7-9, 10-12} 0.46 Q2, Q1 e-c = Beep, beep
{9-7, 12-10} inf Q2, Q1 c-e = Beep, beep
{8-9, 11-12} 0.46 Q2, Q1 b-c = Beep, beep
{9-8, 12-11} inf Q2, Q1 c-b = Beep, beep
.
Resistance measurements Measured with the ohms function
Z 0.0 Fuse - if this is infinite, the fuse is blown or not making contact 1, = fuse is blown
Y inf Safety Interlock, when engaged - if depressing switch does not break contact, the PSU won't run = inf or 1
X 4 inrush limiter when cold = 004
W 160 Primary of filament transformer in 115V config - if open then +5Standby won't be active = 160
V 6 Secondary of filament transformer = 7
U 6 Secondary of filament transformer = 6
And here's a picture form of it
https://www.dropbox.com/scl/fi/v1pfzro0q2zqv56hqhkia/My-Lisa-PSU-measurements.png?rlkey=sw00fjdgkmag5k0u9fim3chld&st=rn2p7x9u&dl=0
edit by sigma7: fixed my mistake mislabeling CR20a/b
Quote from: berskyboy on September 17, 2026, 10:15:21 AMhere's my readings
Diodes Fwd, Rev Description My PSU Measurements
{AA, AB} 0.46, inf CR18, CR19 = AA Beep, Beep: AB: beep
In this list of readings, what does "Beep" indicate? If there is no reading on the display, please check the DMM manual. Perhaps it means "low battery" and you need to replace the DMM's battery to get these readings.
Quote from: sigma7 on September 17, 2026, 11:35:03 AMIn this list of readings, what does "Beep" indicate? If there is no reading on the display, please check the DMM manual. Perhaps it means "low battery" and you need to replace the DMM's battery to get these readings.
Like a short, I was using the continuity test
Quote from: berskyboy on September 17, 2026, 12:04:06 PMQuote from: sigma7 on September 17, 2026, 11:35:03 AMwhat does "Beep" indicate?
Like a short, I was using the continuity test
By "continuity test" I presume you mean the "diode test", often considered the same thing by some meters. Other meters (typically only expensive ones) have a separate continuity function that beeps, and a diode test function that doesn't.
Ah ok. The beep isn't precise enough to determine a short in this case. For example, {BA, BB} (which is CR20, not CR18/19 as I originally wrote) has a low junction voltage around 0.13V, so your particular meter may show 130 and beep, but it is not a short circuit. (Or maybe it shows 000 and it is a short circuit.) In this case we can be confident it is not a short circuit, as it does not beep when the leads are reversed.
Please re-check the beep readings and update them with the digits on the display.
Quote from: sigma7 on September 17, 2026, 03:08:29 PMBy "continuity test" I presume you mean the "diode test", often considered the same thing by some meters. Other meters (typically only expensive ones) have a separate continuity function that beeps, and a diode test function that doesn't.
Ah ok. The beep isn't precise enough to determine a short in this case. For example, {BA, BB} (which is CR20, not CR18/19 as I originally wrote) has a low junction voltage around 0.13V, so your particular meter may show 130 and beep, but it is not a short circuit. (Or maybe it shows 000 and it is a short circuit.) In this case we can be confident it is not a short circuit, as it does not beep when the leads are reversed.
Please re-check the beep readings and update them with the digits on the display.
I rechecked those measurements and have this as the following:
Diodes Fwd, Rev Description My PSU Measurements
{AA, AB} 0.46, inf CR18, CR19 AA: inf, inf, AB: 0,0.1
{BA, BB} 0.13, inf CR18, CR19 BA: 127, climbing to inf, BB: 126, climbing to inf
{CA, CB, CC, CD} 0.5, inf CR1, CR2, CR3, CR4 CA: 550,530, CB: 530,522 CC: 526, 524, CD: 525, 534
{DA, DB} 0.30, 0.37 CR25, CR23 DA: 300,300 DB: 298,333
{EA, EB} 0.38, inf CR26, CR24 EA: 417,inf EB: 420,inf
{FA, FB} 0.41, inf CR22, CR21 FA: 417,inf FB: 417, inf
.
Transistors
Red-Blk Description
{1-2, 4-5} 1.25 Q4, Q3 c-b 1863, 1864
{2-1, 5-4} 0.62 Q4, Q3 b-c 766, 762
{1-3, 4-6} 0.70 Q4, Q3 c-e 961, 1044
{3-1, 6-4} 1.89 Q4, Q3 e-c 1580 then 1, 1844 then 1
{2-3. 5-6} 0.64 Q4, Q3 b-e 744, 747
{3-2, 6-5} inf Q4, Q3 e-b 1987 then 1, 1897 then 1
{7-8, 10-11} 0.00 Q2, Q1 e-b (in parallel with pulse transformer) Inf, 0
{8-7, 11-10} 0.00 Q2, Q1 b-e (in parallel with pulse transformer) 0, 0
{7-9, 10-12} 0.46 Q2, Q1 e-c 1v, Inf (circle), 0v inf (circle)
{9-7, 12-10} inf Q2, Q1 c-e 0v, 0v
{8-9, 11-12} 0.46 Q2, Q1 b-c 0v, 2v
{9-8, 12-11} inf Q2, Q1 c-b 0v, 0v and 1-2v (circle)
.
Resistance measurements Measured with the ohms function
Z 0.0 Fuse - if this is infinite, the fuse is blown or not making contact 1, fuse is blown
Y inf Safety Interlock, when engaged - if depressing switch does not break contact, the PSU won't run
X 4 inrush limiter when cold 004
W 160 Primary of filament transformer in 115V config - if open then +5Standby won't be active 160
V 6 Secondary of filament transformer 7
U 6 Secondary of filament transformer 6
I'm not sure how to measure 9 and 12 (there is a circle and then a centre, I measured both)
https://www.dropbox.com/scl/fi/4kmjfg2s54hulio5a98p7/Screenshot-2026-09-17-at-2.37.47-PM.png?rlkey=sugmcbhju5hfg42bz2p12gutl&st=841ehd7b&dl=0
https://www.dropbox.com/scl/fi/i34dgwvpmminjtan71i0y/IMG_3494.jpeg?rlkey=34mzeq2ey5wc847gwy2n8j90u&st=m2xel7le&dl=0
thanks so much for your help. I'm sorry my reading skills are not perfect. I'm still learning :)
Quote from: berskyboy on September 17, 2026, 04:41:19 PMI'm not sure how to measure 9 and 12 (there is a circle and then a centre, I measured both)
Sorry about the ambiguous circle, apply the probe to the solder portion.
QuoteI rechecked those measurements
{AA, AB} 0.46, inf CR18, CR19 AA: inf, inf, AB: 0,0.1
AA being inf in both directions seems like a measurement problem, like not making good contact.
Please check AA and AB again in both directions.
Quote{7-9, 10-12} 0.46 Q2, Q1 e-c 1v, Inf (circle), 0v inf (circle)
{9-7, 12-10} inf Q2, Q1 c-e 0v, 0v
{8-9, 11-12} 0.46 Q2, Q1 b-c 0v, 2v
{9-8, 12-11} inf Q2, Q1 c-b 0v, 0v and 1-2v (circle)
Part of this implies Q2 is in the area of the problem, and part implies Q1 is in the area of the problem. Please double check these.
I'm not saying the measurements are wrong necessarily, I just don't have a theory yet as to how this combination could happen.
Quotethanks so much for your help. I'm still learning :)
You're welcome... time will tell if it actually is helpful :)
We are all still learning.
Quote from: sigma7 on September 17, 2026, 05:19:56 PMAA being inf in both directions seems like a measurement problem, like not making good contact.
Please check AA and AB again in both directions.
Quote{7-9, 10-12} 0.46 Q2, Q1 e-c 1v, Inf (circle), 0v inf (circle)
{9-7, 12-10} inf Q2, Q1 c-e 0v, 0v
{8-9, 11-12} 0.46 Q2, Q1 b-c 0v, 2v
{9-8, 12-11} inf Q2, Q1 c-b 0v, 0v and 1-2v (circle)
Part of this implies Q2 is in the area of the problem, and part implies Q1 is in the area of the problem. Please double check these.
I'm not saying the measurements are wrong necessarily, I just don't have a theory yet as to how this combination could happen.
Measurement
{AA, AB} 0.46, inf CR18, CR19 AA: 0,0 AB: inf,0
{7-9, 10-12} 0.46 Q2, Q1 e-c 0, 0 or 1
{9-7, 12-10} inf Q2, Q1 c-e 0,0
{8-9, 11-12} 0.46 Q2, Q1 b-c 0,0
{9-8, 12-11} inf Q2, Q1 c-b 0, 0
Quote from: berskyboy on September 17, 2026, 07:09:36 PM{AA, AB} 0.46, inf CR18, CR19 AA: 0,0 AB: inf,0
{7-9, 10-12} 0.46 Q2, Q1 e-c 0, 0 or 1
{9-7, 12-10} inf Q2, Q1 c-e 0,0
{8-9, 11-12} 0.46 Q2, Q1 b-c 0,0
{9-8, 12-11} inf Q2, Q1 c-b 0, 0
Anyone following along have a theory as to what this sequence of readings mean?
Both Q1 and Q2 shorted c-e or some DMM artifact?
Quote from: berskyboy on September 17, 2026, 07:09:36 PM{AA, AB} 0.46, inf CR18, CR19 AA: 0,0 AB: inf,0
{7-9, 10-12} 0.46 Q2, Q1 e-c 0, 0 or 1
{9-7, 12-10} inf Q2, Q1 c-e 0,0
{8-9, 11-12} 0.46 Q2, Q1 b-c 0,0
{9-8, 12-11} inf Q2, Q1 c-b 0, 0
Please:
- confirm those measurements were made with the diode test function (if not, repeat using diode test), and
- repeat those measurements using the 200 ohm resistance mode of the DMM (so we have both the diode test and resistance measurements).
Quote from: sigma7 on September 17, 2026, 08:44:24 PMQuote{AA, AB} 0.46, inf CR18, CR19 AA: 0,0 AB: inf,0
{7-9, 10-12} 0.46 Q2, Q1 e-c 0, 0 or 1
{9-7, 12-10} inf Q2, Q1 c-e 0,0
{8-9, 11-12} 0.46 Q2, Q1 b-c 0,0
{9-8, 12-11} inf Q2, Q1 c-b 0, 0
Please:
- confirm those measurements were made with the diode test function (if not, repeat using diode test), and
- repeat those measurements using the 200 ohm resistance mode of the DMM (so we have both the diode test and resistance measurements).
Diodes Fwd, Rev Description My PSU Measurements (200ohm) Diode Test
{AA, AB} 0.46, inf CR18, CR19 AA: 0,0 AB: inf,0 AA: 4 with beep, 4 with beep AB: 3 with beep, 3 with beep
{7-9, 10-12} 0.46 Q2, Q1 e-c 0.6, 0.6 2 with beep, 2 with beep
{9-7, 12-10} inf Q2, Q1 c-e 0.4,0.4 3 with beep, 2 with beep
{8-9, 11-12} 0.46 Q2, Q1 b-c 0.6, 0.5 2 with beep, 2 with beep
{9-8, 12-11} inf Q2, Q1 c-b 0.4, 0.4 2 with beep, 2 with beep
------
I was checking and found some replacement parts of the Q1 and Q2
https://canada.newark.com/webapp/wcs/stores/servlet/PFOrderCopy?orderId=RSyKGa2mSQ3syebQmY0AnBBWBThEJa2bnxY7%2fJ%2b0eR4%3d_IBM_2&langId=1&storeId=10196&catalogId=15003&URL=AjaxOrderItemDisplayView&CMP=e-email-sys-sendbask-GLB
Unless you want to stock spare parts, it is probably best to determine exactly which components need replacement before ordering any.
To investigate further:
Desolder one end of CR18 and lift that end slightly from the circuit board. You only need to tilt it up enough that the end of the desoldered lead clears the hole in the board. One way to do this is to put a small screwdriver under one lead (on the component side of the board), and apply gentle leverage while heating the solder joint. If you use too much force, the component will break.
On this particular product, most of the component leads are bent over on the bottom before soldering. The lead that is less bent over will be easier to extract. In some cases, one needs to melt and remove as much solder as practical then straighten the lead where it is bent over on the bottom, then proceed to try to reheat and extract it.
If you have any trouble or are in doubt, post pictures of what you've got.
Once this is done, CR18 is only connected at one end, the other end is up in the air.
Then, using the diode test:
- On the component side, measure CR18 in both directions, and
- On the bottom side, measure between pads 10-12 (red-black), and
- On the bottom side, measure between pads 12-10 (red-black)
Quote from: sigma7 on September 18, 2026, 02:52:58 PMOnce this is done, CR18 is only connected at one end, the other end is up in the air.
Then, using the diode test:
- On the component side, measure CR18 in both directions, and
- On the bottom side, measure between pads 10-12 (red-black), and
- On the bottom side, measure between pads 12-10 (red-black)
1. On the component side, measure CR18 in both directions, and. = (Red to Black = 1, Black to Red 549)
2. On the bottom side, measure between pads 10-12 (red-black), = 0.5, and 2 with beep in diode mode
3. On the bottom side, measure between pads 12-10 (red-black), = 0.5 , 2 with beep in diode mode
Excellent, that suggests CR18 is good. Leave it disconnected for now.
To further investigate Q1, on the component side of the board, beside CR18 locate Q1 (the silver part on a trapezoid shaped heatsink, (close to the big transformer with the copper wrap). Try removing the one phillips head screw attaching Q1 that is further from the edge of the board. If it just spins, stop trying and we will do something else.
If you can remove the screw, use the diode test to measure between 10-12 and 12-10 on the bottom side.
Quote from: sigma7 on September 18, 2026, 03:54:44 PMIf you can remove the screw, use the diode test to measure between 10-12 and 12-10 on the bottom side.
between 10-12 and 12-10 = 0 coz the screw is removed. The screw to remove should be closest to CR18?
with the screw closes to CR18 removed
between 10-12 and 12-10 = 2 with beep, and 2 with beep
Quote from: berskyboy on September 18, 2026, 04:10:09 PMQuote from: sigma7 on September 18, 2026, 03:54:44 PMIf you can remove the screw, use the diode test to measure between 10-12 and 12-10 on the bottom side.
between 10-12 and 12-10 = 0 coz the screw is removed. The screw to remove should be closest to CR18?
The screw to be removed is farther from CR18, even better if you can remove both screws without difficulty, then use the diode test to check 10-12 and 12-10.
Quote from: sigma7 on September 18, 2026, 04:13:20 PMThe screw to be removed is farther from CR18, even better if you can remove both screws without difficulty, then use the diode test to check 10-12 and 12-10.
with the screw removed you are not testing to a contact. (open circuit gives 1 on DMM). Did you mean 10 to 11? 10-11 gives 2 with beep
Quote from: berskyboy on September 18, 2026, 04:17:38 PMwith the screw removed you are not testing to a contact.
With the screw removed, you should see: an empty hole, and around the hole is a solder ring, with a copper trace (under the green solder mask) that makes a short dog-leg to another solder pad about 0.5" or 1cm away. The solder ring around the hole is where the probe should make contact.
The intent is to measure what remains once Q1 is partially removed from the circuit.
So I expect that's what you did and when you measured 10-12 and 12-10, you found it was open circuit, that's fine. (Correct me/re-measure if I'm mistaken).
Then measure from 10 on the bottom side to the silver metal case of Q1 on the top side.
Quote from: sigma7 on September 18, 2026, 04:35:39 PMSo I expect that's what you did and when you measured 10-12 and 12-10, you found it was open circuit, that's fine. (Correct me/re-measure if I'm mistaken).
Then measure from 10 on the bottom side to the silver metal case of Q1 on the top side.
correct open circuit DMM = 1
from 10 to the case (Red 10 to Black case) = 2 plus beep , 10 (Black to case) beeps and sporadic measurements
Ok, let's compare with Q2.
Try removing the phillips screw closest to the edge of the board that is attaching Q2.
Then using the diode test, measure:
AB in both directions
7-9 in both directions
Quote from: sigma7 on September 18, 2026, 04:51:46 PMAB in both directions
7-9 in both directions
AB in both directions = 561, 1 (inf?)
7-9 in both directions = 2 with beep, 2 with beep
Ok, it looks like both Q1 and Q2 are bad. You should remove them and test them out of circuit entirely.
Start by marking the cases of Q1 and Q2 with a marker or tape so you can keep track of which is which.
With all 4 phillips screws removed, each of Q1 and Q2 has 2 leads soldered to the board.
Once the leads are desoldered, slowly/carefully remove one of the transistors. If the heatsink comes with it, you can leave it stuck together; watch out for insulating nylon washers under the heatsink's screw holes. Otherwise (if the heatsink remains attached to the circuit board), there is a thin mica insulator stuck between the transistor and the black heatsink. The insulator is fragile and there is a thin coating of thermally conductive grease on both sides; it may remain stuck to the heatsink or come off with the transistor, or be stuck to both of them and be at risk of breaking. If you can keep the grease clean, then you won't have to do as much work to reassemble, so avoid touching it.
Once the transistor is removed, use the diode test and check all 6 permutations:
Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
Lead 1 to case
case to Lead 1
Lead 2 to case
case to Lead 2
After the measurements, put the transistor and mica insulator back on the heatsink and circuit board (with insulating nylon washers if present) and insert the screws (slightly tight) to keep everything clean and not lose anything.
Repeat with the other transistor and measure it out of circuit the same way:
Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
Lead 1 to case
case to Lead 1
Lead 2 to case
case to Lead 2
Quote from: sigma7 on September 18, 2026, 05:08:49 PMOnce the transistor is removed, use the diode test and check all 6 permutations:
Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
Lead 1 to case
case to Lead 1
Lead 2 to case
case to Lead 2
After the measurements, put the transistor and mica insulator back on the heatsink and insert the screws (slightly tight) to keep everything clean and not lose anything.
Repeat with the other transistor and measure it out of circuit the same way:
Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
Lead 1 to case
case to Lead 1
Lead 2 to case
case to Lead 2
Q1
Red to Black
Lead 1 to Lead 2 = 2 beep
Lead 2 to Lead 1 = 2 beep
Lead 1 to case = 3 beep
case to Lead 1 = 3 beep
Lead 2 to case = 3 beep
case to Lead 2 = 4 beep
Q2
Red to Black
Lead 1 to Lead 2 = 3 beep
Lead 2 to Lead 1 = 3 beep
Lead 1 to case = 4 beep
case to Lead 1 = 4beep
Lead 2 to case = 3 beep
case to Lead 2 = 4 beep
To me, it is odd that all 3 leads are shorted together, please re-check using the 200 ohm resistance mode.
One of the transistors is enough to confirm.
Quote from: sigma7 on September 18, 2026, 05:49:18 PMTo me, it is odd that all 3 leads are shorted together, please re-check using the 200 ohm resistance mode.
One of the transistors is enough to confirm.
Q1
Red to Black
Lead 1 to Lead 2 = 0.4
Lead 2 to Lead 1 = 0.5
Lead 1 to case = 0.6
case to Lead 1 = 0.7
Lead 2 to case = 0.6
case to Lead 2 = 1.5
Q2
Red to Black
Lead 1 to Lead 2 = 1.2
Lead 2 to Lead 1 = 1.2
Lead 1 to case = inf
case to Lead 1 = inf
Lead 2 to case = inf
case to Lead 2 = inf
Quote from: berskyboy on September 18, 2026, 05:38:33 PMQ2
Red to Black
Lead 1 to case = 4 beep
case to Lead 1 = 4beep
Lead 2 to case = 3 beep
case to Lead 2 = 4 beep
Quote from: berskyboy on September 18, 2026, 06:04:26 PMQ2
Red to Black
Lead 1 to case = inf
case to Lead 1 = inf
Lead 2 to case = inf
case to Lead 2 = inf
These two sets of readings don't agree with each other.
The diode/continuity test says these are a short circuit, and the ohms test says these are an open circuit.
Can you figure out why? I presume the issue is my instructions are ambiguous in some way.
I see the meters from that company do contain fuses, so perhaps the fuse is in the ohms circuit... if you touch the DMM leads together does it show a short circuit in both diode test and 200 ohms resistance modes?
Quote from: sigma7 on September 18, 2026, 06:10:26 PMQuote from: berskyboy on September 18, 2026, 05:38:33 PMQ2
Red to Black
Lead 1 to case = 4 beep
case to Lead 1 = 4beep
Lead 2 to case = 3 beep
case to Lead 2 = 4 beep
Quote from: berskyboy on September 18, 2026, 06:04:26 PMQ2
Red to Black
Lead 1 to case = inf
case to Lead 1 = inf
Lead 2 to case = inf
case to Lead 2 = inf
These two sets of readings don't agree with each other.
The diode/continuity test says these are a short circuit, and the ohms test says these are an open circuit.
Can you figure out why? I presume the issue is my instructions are ambiguous in some way.
I see the meters from that company do contain fuses, so perhaps the fuse is in the ohms circuit... if you touch the DMM leads together does it show a short circuit in both diode test and 200 ohms resistance modes?
two leads together beeps and shows 002 in diode tests
and 0.3 in 200 ohm (no beep)
Quote from: berskyboy on September 18, 2026, 06:23:37 PMQuote from: sigma7 on September 18, 2026, 06:10:26 PMQuote from: berskyboy on September 18, 2026, 05:38:33 PMQ2
Red to Black
Lead 1 to case = 4 beep
case to Lead 1 = 4beep
Lead 2 to case = 3 beep
case to Lead 2 = 4 beep
Quote from: berskyboy on September 18, 2026, 06:04:26 PMQ2
Red to Black
Lead 1 to case = inf
case to Lead 1 = inf
Lead 2 to case = inf
case to Lead 2 = inf
These two sets of readings don't agree with each other.
The diode/continuity test says these are a short circuit, and the ohms test says these are an open circuit.
Can you figure out why? I presume the issue is my instructions are ambiguous in some way.
I see the meters from that company do contain fuses, so perhaps the fuse is in the ohms circuit... if you touch the DMM leads together does it show a short circuit in both diode test and 200 ohms resistance modes?
two leads together beeps and shows 002 in diode tests
and 0.3 in 200 ohm (no beep)
Perhaps one of the DMM leads is intermittent? Inspect them for damage, and in diode test mode, while connected together, wiggle and apply tension to all parts of the leads around to see if you can get the reading to change.
Q2
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = inf, inf
case to Lead 1 = inf , inf
Lead 2 to case = inf Beep , inf
case to Lead 2 = 4 Beep, inf
case meaning the top of the can?
having a hard time with the measurements
Quote from: berskyboy on September 18, 2026, 06:35:45 PMQ2
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = 3B, inf
case to Lead 1 = 3B , inf
These don't agree... diode test shows short, 200 ohms says not short.... if not the DMM leads, perhaps the rotary switch of the DMM doesn't always make good contact?
Today at 06:35:45 PM
Last Edit: Today at 06:45:36 PM by berskyboy
Q2
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = inf, inf
case to Lead 1 = inf , inf
Lead 2 to case = inf Beep , inf
case to Lead 2 = 4 Beep, inf
case meaning the top of the can?
having a hard time with the measurements
Quote from: berskyboy on September 18, 2026, 06:46:01 PMcase meaning the top of the can?
Case meaning the silvery part of the transistor, so not the black heatsink (if still attached), not a surface with the thermal grease on it (if any is showing). The case is any part of the silvery domed cylinder and the trapezoid plate with screw holes it is attached to.
Perhaps there is oxidization or corrosion or some other contamination on the surface that you need to scratch through to make good contact.
Q2
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = 2 beep, 0.6
case to Lead 1 = 3 beep, 0.6
Lead 2 to case = 3 beep,1.6
case to Lead 2 = inf, inf
Quote from: berskyboy on September 18, 2026, 07:02:56 PMLead 2 to case = 3 beep,1.6
case to Lead 2 = inf, inf
Again, the lack of symmetry between short and open circuit measurements indicates a measurement problem.
Dunno what to say... keep fiddling with it until you figure out how to get consistent results... it may be the DMM, the leads, poor contact between the probes and the device...
Q1
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = inf beep, inf
case to Lead 1 = 2 beep, 0.4
Lead 2 to case = 3 beep,1.2
case to Lead 2 = 2beep, 0.5
I can try and buy another DMM, this one might be cheap?
Q2
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = 5 beep ,1.2
case to Lead 1 = 6 beep, 1.6
Lead 2 to case = 3 beep ,0.7
case to Lead 2 = 3 beep,1.5
Quote from: berskyboy on September 18, 2026, 07:11:38 PMI can try and buy another DMM, this one might be cheap?
If you're having trouble getting consistent results, that seems like a good option. Then you've got two to compare if something looks odd.
As it is, unreliable measurements aren't very useful and it is hard to know how to proceed with troubleshooting. If you can figure out how to make the measurements repeatable/reliable say 10 times in a row, then post what you get, and explain what you figured out that you needed to do to get reliable results. (Without an explanation of what was wrong, future measurements remain suspect.)
Quote from: sigma7 on September 18, 2026, 07:25:16 PMIf you're having trouble getting consistent results, that seems like a good option. Then you've got two to compare if something looks odd.
As it is, unreliable measurements aren't very useful and it is hard to know how to proceed with troubleshooting. If you can figure out how to make the measurements repeatable/reliable say 10 times in a row, then post what you get, and explain what you figured out that you needed to do to get reliable results. (Without an explanation of what was wrong, future measurements remain suspect.)
ok sounds good. Do you recommend a certain brand?
I got a new DMM let's try this again (I can try taking more measurements tomorrow).
Q1
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = 0L,0L
case to Lead 1 = 0.5, 0L
Lead 2 to case = erratic
case to Lead 2 = 0L
Q1
Red to Black. (diode test, 200 ohm test)
Lead 1 to case = 0L, 0L
case to Lead 1 = 0L, 0L
Lead 2 to case = 0L,0L
case to Lead 2 = 0L,0L
Quote from: berskyboy on September 18, 2026, 11:50:31 PMI got a new DMM let's try this again
Excellent; to see how it behaves compared to the other one, try these measurements again using the diode test mode:
| Diodes | Fwd, Rev | Description |
| {BA, BB} | 0.13, inf | CR20a, CR20b |
| {DA, DB} | 0.30, 0.37 | CR25, CR23 |
| . |
| Transistors | Red-Blk | Description |
| {1-2, 4-5} | 1.25 | Q4, Q3 c-b |
| {2-1, 5-4} | 0.62 | Q4, Q3 b-c |
| {1-3, 4-6} | 0.70 | Q4, Q3 c-e |
| {3-1, 6-4} | 1.89 | Q4, Q3 e-c |
| {2-3. 5-6} | 0.64 | Q4, Q3 b-e |
| {3-2, 6-5} | inf | Q4, Q3 e-b |
|
And for each of Q1 and Q2 now out of circuit, also measure
Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
QuoteQ1
Lead 2 to case = erratic
"erratic" implies a bad probe connection. Perhaps there is another explanation, but first try again and see if pressing the probes more firmly against the transistor makes the reading stable.
Also, avoid touching both points of contact while taking the measurement. eg. don't 'clamp' each of the probes against the transistor leads using thumb and finger touching the metal parts. You could squeeze one of the probes against a lead, but the other should not have a conductive path to you, as the current path through your skin can affect some readings. If you can avoid touching both, then thats the best option.
Quote from: sigma7 on September 19, 2026, 05:20:40 AMExcellent; to see how it behaves compared to the other one, try these measurements again using the diode test mode:
Diodes Fwd, Rev Description Measurement
{BA, BB} 0.13, inf CR20a, CR20b BA: 0, OL BB: 0,OL
{DA, DB} 0.30, 0.37 CR25, CR23 DA: OL,OL DB:
.
I stopped because should I put Q1 and Q2 back into the PSU?
And for each of Q1 and Q2 now out of circuit, also measure
Q1
Red to Black
Lead 1 to Lead 2. 0
Lead 2 to Lead 1 0.1
Q2
Red to Black
Lead 1 to Lead 2 0.8
Lead 2 to Lead 1 0.6
Quote from: berskyboy on September 19, 2026, 12:04:22 PMQuote from: sigma7 on September 19, 2026, 05:20:40 AMExcellent; to see how it behaves compared to the other one, try these measurements again using the diode test mode:
I stopped because should I put Q1 and Q2 back into the PSU?
No, make these measurements with Q1 and Q2 removed, but that is a good question.
QuoteDiodes Fwd, Rev Description Measurement
{BA, BB} 0.13, inf CR20a, CR20b BA: 0, OL BB: 0,OL
{DA, DB} 0.30, 0.37 CR25, CR23 DA: OL,OL DB:
And for each of Q1 and Q2 now out of circuit, also measure
Q1
Red to Black
Lead 1 to Lead 2. 0
Lead 2 to Lead 1 0.1
Q2
Red to Black
Lead 1 to Lead 2 0.8
Lead 2 to Lead 1 0.6
Are those measurements using a "diode test" function? From the readings I'd guess it was a resistance mode.
So I can peruse the manual, what is the brand and model of DMM you are using now?
Quote from: sigma7 on September 19, 2026, 01:33:42 PMAre those measurements using a "diode test" function? From the readings I'd guess it was a resistance mode.
So I can peruse the manual, what is the brand and model of DMM you are using now?
Here's a photo of it. ASTrOAI CM2KOR
https://www.dropbox.com/scl/fi/2giwzufwhe0l051stcxix/ASTrOAI.HEIC?rlkey=b7got1wh776cwtdchmoxarybb&st=i8ld7461&dl=0
that was in diode mode.
Quote from: berskyboy on September 19, 2026, 02:52:45 PMHere's a photo of it. ASTrOAI CM2KOR
https://www.dropbox.com/scl/fi/2giwzufwhe0l051stcxix/ASTrOAI.HEIC?rlkey=b7got1wh776cwtdchmoxarybb&st=i8ld7461&dl=0
that was in diode mode.
Test CR18 on the component side (one end still disconnected from the board) in both directions using the diode test mode.
Note the manual (https://ca.astroai.com/digital-clamp-meter-multimeter-2000-counts-cm2k0r/ap/10001485#:~:text=CM2K0R%20User%20Manual-,English,-Deutsch) says on page 17 that to enter Diode Test mode, you have to press the "Func" button after rotating the switch to the diode test/continuity position. When in that mode, the diode symbol will be shown in the display.
Quote from: sigma7 on September 19, 2026, 02:57:02 PMTest CR18 on the component side (one end still disconnected from the board) in both directions using the diode test mode.
CR18 in diode mode
OL, OL
CR18 in resistance ohm mode
33.4, 0.45
Quote from: berskyboy on September 19, 2026, 03:04:53 PMQuote from: sigma7 on September 19, 2026, 02:57:02 PMTest CR18 on the component side (one end still disconnected from the board) in both directions using the diode test mode.
CR18 in diode mode
OL, OL
Did you see the edit I made that says "Note the manual says on page 17 that to enter Diode Test mode, you have to press the "Func" button after rotating the switch to the diode test/continuity position. When in that mode, the diode symbol will be shown in the display."?
If not, try the test again in diode test mode.
thank you for that
CR18 in diode mode
0.462V, OL
Quote from: berskyboy on September 19, 2026, 03:11:55 PMthank you for that
My pleasure.
Test Q1 and Q2 again, out of circuit, use the diode test and check all 6 permutations:
Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
Lead 1 to case
case to Lead 1
Lead 2 to case
case to Lead 2
Quote from: sigma7 on September 19, 2026, 05:20:40 AM| Diodes | Fwd, Rev | Description |
| {BA, BB} | 0.13, inf | CR20a, CR20b |
| {DA, DB} | 0.30, 0.37 | CR25, CR23 |
| . |
| Transistors | Red-Blk | Description |
| {1-2, 4-5} | 1.25 | Q4, Q3 c-b |
| {2-1, 5-4} | 0.62 | Q4, Q3 b-c |
| {1-3, 4-6} | 0.70 | Q4, Q3 c-e |
| {3-1, 6-4} | 1.89 | Q4, Q3 e-c |
| {2-3. 5-6} | 0.64 | Q4, Q3 b-e |
| {3-2, 6-5} | inf | Q4, Q3 e-b |
|
And for each of Q1 and Q2 now out of circuit, also measure
Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
Now my new measurements:
Diodes Fwd, Rev Description My Measurement
{BA, BB} 0.13, inf CR20a, CR20b BA: 0.126, climbing BB: 0.126,climbinng
{DA, DB} 0.30, 0.37 CR25, CR23 DA: 0.26, 0.277 DB: 0.267, 0.260
Transistors Red-Blk Description. My Measurement:
{1-2, 4-5} 1.25 Q4, Q3 c-b. 0.775, 0.767
{2-1, 5-4} 0.62 Q4, Q3 b-c. 0.572, 0.566
{1-3, 4-6} 0.70 Q4, Q3 c-e. 0.661, 0.681
{3-1, 6-4} 1.89 Q4, Q3 e-c. 1.583, 1.585
{2-3. 5-6} 0.64 Q4, Q3 b-e. 0.612, 0.618
{3-2, 6-5} inf Q4, Q3 e-b. 1.712, 1.725
Q1
Red to Black
Lead 1 to Lead 2. 0v
Lead 2 to Lead 1 OL
Q2
Red to Black
Lead 1 to Lead 2 0v
Lead 2 to Lead 1 0v
Quote from: sigma7 on September 19, 2026, 03:14:23 PMTest Q1 and Q2 again, out of circuit, use the diode test and check all 6 permutations:
Red to Black
Lead 1 to Lead 2
Lead 2 to Lead 1
Lead 1 to case
case to Lead 1
Lead 2 to case
case to Lead 2
Q1
Red to Black
Lead 1 to Lead 2 0v
Lead 2 to Lead 1 OL
Lead 1 to case 0v
case to Lead 1 0v
Lead 2 to case 0v
case to Lead 2 0v
Q2
Red to Black
Lead 1 to Lead 2 0v
Lead 2 to Lead 1. 0v
Lead 1 to case 0v
case to Lead 1 0v
Lead 2 to case 0v
case to Lead 2 0v
Quote from: berskyboy on September 19, 2026, 03:31:55 PMQuote from: sigma7 on September 19, 2026, 03:14:23 PMTest Q1 and Q2 again, out of circuit, use the diode test:
Q1
Red to Black
Lead 1 to Lead 2 0v
Lead 2 to Lead 1 OL
Check this again, if it is a short circuit, it should be bidirectional.
With Q1 and Q2 and CR18 still out of circuit, do these again using the diode test (we are looking for additional problems):
| Diodes | Fwd, Rev | Description |
| {AA, AB} | 0.46, inf | CR18, CR19 |
| {BA, BB} | 0.13, inf | CR20a, CR20b |
| {CA, CB, CC, CD} | 0.5, inf | CR1, CR2, CR3, CR4 |
| {DA, DB} | 0.30, 0.37 | CR25, CR23 |
| {EA, EB} | 0.38, inf | CR26, CR24 |
| {FA, FB} | 0.41, inf | CR22, CR21 |
| . |
| Transistors |
| Red-Blk | | Description |
| {1-2, 4-5} | 1.25 | Q4, Q3 c-b |
| {2-1, 5-4} | 0.62 | Q4, Q3 b-c |
| {1-3, 4-6} | 0.70 | Q4, Q3 c-e |
| {3-1, 6-4} | 1.89 | Q4, Q3 e-c |
| {2-3. 5-6} | 0.64 | Q4, Q3 b-e |
| {3-2, 6-5} | inf | Q4, Q3 e-b |
Oh maybe you just did that... wait while I review
Quote from: sigma7 on September 19, 2026, 04:20:34 PMOh maybe you just did that... wait while I review
Most looks good.
Quote from: berskyboy on September 19, 2026, 03:31:55 PMQuote from: sigma7 on September 19, 2026, 03:14:23 PMTest Q1 and Q2 again, out of circuit, use the diode test:
Q1
Red to Black
Lead 1 to Lead 2 0v
Lead 2 to Lead 1 OL
Check this again, if it is a short circuit, it should be bidirectional.
With Q1 and Q2 and CR18 still out of circuit, do these again using the diode test (we are looking for additional problems):
| Diodes | Fwd, Rev | Description |
| {AA, AB} | 0.46, inf | CR18, CR19 |
| {CA, CB, CC, CD} | 0.5, inf | CR1, CR2, CR3, CR4 |
| {EA, EB} | 0.38, inf | CR26, CR24 |
| {FA, FB} | 0.41, inf | CR22, CR21 |
| . |
| Check the following again with the daughterboard removed: |
| Transistors |
| Red-Blk | | Description |
| {3-2, 6-5} | inf | Q4, Q3 e-b |
Quote from: sigma7 on September 19, 2026, 04:27:33 PMCheck this again, if it is a short circuit, it should be bidirectional.
With Q1 and Q2 and CR18 still out of circuit, do these again using the diode test (we are looking for additional problems):
Morning,
Here's a few more measurements:
{AA, AB} 0.46, inf CR18, CR19 AA:0.469, OL AB: 0.476, OL
{BA, BB} 0.13, inf CR18, CR19 BA: 0.132, climbing BB: 0.132,climbinng
{CA, CB, CC, CD} 0.5, inf CR1, CR2, CR3, CR4 CA: 0.473,OL CB:0.480, OL CC:0.476, OL DC:0.468, OL
{DA, DB} 0.30, 0.37 CR25, CR23 DA: 0.26, 0.277 DB: 0.263, 0.275
{EA, EB} 0.38, inf CR26, CR24 EA: 0.392 , climbing, EB: 0.392, OL
{FA, FB} 0.41, inf CR22, CR21 FA: 0.392, OL FB: 0.391, OL
.
Transistors
Red-Blk Description
{1-2, 4-5} 1.25 Q4, Q3 c-b 0.775, 0.767
{2-1, 5-4} 0.62 Q4, Q3 b-c 0.572, 0.566
{1-3, 4-6} 0.70 Q4, Q3 c-e 0.661, 0.681
{3-1, 6-4} 1.89 Q4, Q3 e-c 1.583, 1.585
{2-3. 5-6} 0.64 Q4, Q3 b-e 0.612, 0.618
{3-2, 6-5} inf Q4, Q3 e-b 1.712, 1.725 // 0.731 , OL
{7-8, 10-11} 0.00 Q2, Q1 e-b (in parallel with pulse transformer) Ov, 0v
{8-7, 11-10} 0.00 Q2, Q1 b-e (in parallel with pulse transformer) 0v, 0v
Quote from: berskyboy on September 21, 2026, 09:36:41 AMHere's a few more measurements
From those, I don't see any obvious issues on the main board with Q1 and Q2 removed from the circuit.
(For future reference, I'm assuming the lower Q4, Q3 c-b measurement is due to a difference in DMM characteristics, and that Q4, Q3 e-b is with the daughterboard installed.)
Temporarily overloading the output is a condition that the PSU design anticipates and normally protects from and survives without damage.
So the likely cause of the failure of Q1 and Q2 is the solder bridge(s). Since a solder bridge is an unusual cause of failure, we can't be confident that Q1 and Q2 are the only components that need to be replaced.
I'll work on some measurement instructions to look for further failures on the daughterboard. In the meantime:
Use the image below to diligently check for any remaining solder bridges. If any remain, then Q1 and Q2 may be destroyed again after replacement, and further parts may be damaged too. Shiny solder joints hide subtle details, so after fully checking it once, it can be helpful to rotate the board and check again from a different angle.
If you find any bridges, take a picture/make a note of where they are as that information can help locate and/or eliminate additional components to suspect.
Quote from: sigma7 on September 21, 2026, 04:49:48 PMI'll work on some measurement instructions to look for further failures on the daughterboard. In the meantime:
Use the image below to diligently check for any remaining solder bridges. If any remain, then Q1 and Q2 may be destroyed again after replacement, and further parts may be damaged too. Shiny solder joints hide subtle details, so after fully checking it once, it can be helpful to rotate the board and check again from a different angle.
If you find any bridges, take a picture/make a note of where they are as that information can help locate and/or eliminate additional components to suspect.
Here's a photo of the board and maybe some solder bridges? I thought the dot close together would be the same join?
https://www.dropbox.com/scl/fi/hw98nypaj0xsqwhhfgoer/Soldure.Bridges.heic?rlkey=sa3nlcvognw0gys8tra246itb&st=dzc64371&dl=0
Remove the daughterboard and check it while disconnected from the main board:
With the black lead on pin 5 of the daughterboard's connector, put the red lead on each of the other connector pins and measure with diode test mode, and again with resistance mode.
Black to Pin 5, Red to Pin x
| Pin x | DiodeTest | Resistance | Signal |
| 1 | inf | 6k | +12 sense |
| 2 | inf | 10k | line sense |
| 3 | 1.1 | >5k | +18V |
| 4 | inf | 50k | on/off |
| - | - | - | ground |
| 6 | inf | 2.6k | +5 sense |
| 7 | inf | 2.5k | current sense |
| 8 | inf | >100k | /shutdown |
| 9 | inf | inf | /power fail |
| 10 | inf | inf | pull |
| 11 | inf | inf | push |
| 12 | 1.1 | >1k | logic +5 |
| 13 | inf | inf | /delay reset |
Quote from: berskyboy on September 21, 2026, 06:41:13 PMHere's a photo of the board and maybe some solder bridges? I thought the dot close together would be the same join?
The red arrows don't point to solder bridges as far as I can tell.
Referring to the black and white diagram, there should not be any solder that bridges across a white gap from one black section to a different black section. It can be very difficult to see a bridge in a photo, so you should look at the narrow white sections and carefully compare to your board.
Quote from: sigma7 on September 21, 2026, 06:48:52 PMWith the black lead on pin 5 of the daughterboard's connector, put the red lead on each of the other connector pins and measure with diode test mode, and again with resistance mode.
Black to Pin 5, Red to Pin x
Pin x DiodeTest Resistance Signal. Measurements
1 inf 6k +12 sense. 1.628
2 inf 10k line sense. 1.842
3 1.1 >5k +18V 0.949
4 inf 50k on/off. OL
- - - ground
6 inf 2.6k +5 sense. 1.196
7 inf 2.5k current sense. 1.163
8 inf >100k /shutdown. OL
9 inf inf /power fail. OL
10 inf inf pull. OL
11 inf inf push. OL
12 1.1 >1k logic +5. 0.871
13 inf inf /delay reset. OL
sigma7, are you a human?
I am growing more-and-more suspicious that you may be not:
You've been guiding berskyboy relentlessly to fix his power supply.
You've been posting voltage measurements of a working power supply, photos and custom-made schematics. I have't seen such level of dedication in humans...
Kudos if you are!
Piling on to say the same. What a heroic effort!
Yes I know for sure I'm 100% grateful!! Plan B would be this clone PSU,
https://68kmla.org/bb/threads/lisa-1-8a-psu-clone-by-warmech.47154/page-2
but I am still hopping to get the old gal running. LOL. Lisa would be a girl right?
The short circuit of Q1 and Q2 would result in a current having most of the available energy from the main capacitors (plus more from the power utility until the fuse blew).
This current goes through windings of pulse transformers T4 and T5, so we need to check that there is still continuity through those windings.
Refer to the drawing, and measure the resistance between each of these pairs (Q1 and Q2 still removed from the circuit):
T4:5 - T4:6
T5:5 - T5:6
In each case, the resistance should be close to 0.0 ohms.
Normally, with Q1 and Q2 out of circuit (either completely, or with the 4 phillips head mounting screws removed such that their cases are disconnected), the main transformer will not receive any switching current.
In this state, the only output voltage will be +5Standby.
With the high power circuitry inactive, we can (hopefully) check some of the control circuitry without having a fault in the high power circuitry blowing the fuse.
Double check that Q1 and Q2 are disconnected (4 screws removed) or completely removed from the circuit board.
Ensure a good fuse is installed.
Connect the test jig load circuit to the card edge, and turn its small switch "off".
Connect the line power and turn on the power strip; there should not be any smoke, flashes, odours, blown fuse or other dramatic evidence of something happening. If something does, stop here, disconnect the power and report what you observed.
If Q1 is still mounted on the board, measure the DC voltage from its case to ground. If the voltage exceeds 1 Volt, immediately remove power and stop here.
The small switch should still be in the OFF position, and the power strip will be on. Check the DC and AC voltages from pin 3 of the daughterboard connector to ground. This should be about 16 to 18V DC, and should have an AC voltage of less than 1V; if the DC and AC voltage are in that range, continue with the next step. If not, stop here, remove power, and report what you observed. If the DC voltage is about half or double, investigate whether the 115/230V jumpers are not installed correctly or damaged or not making proper contact. If the DC voltage was zero, check the fuse.
Remember to set the meter back to DC volts after measuring the AC volts.
Check the DC voltage across R33 (from one end to the other, not to ground) & across R2. (These are two large resistors beside the large black capacitor C8.) They should be about 150-170 V each (positive or negative, depending on which way you probe them): if so, continue with the next step. If not, then the primary rectifier, line filter, and associated components are suspect - stop here, remove power, and report what you observed.
Check the DC voltage at pin 12 of the daughterboard connector to ground. This should be about 5V: if so, continue with the next step. If not then Z2 on the daughterboard is suspect - stop here, remove power, and report what you observed.
Make sure the interlock switch has been engaged. Set the small switch (on the test jig connected to the card edge) to the ON position. There should not be any smoke, flashes, odours, blown fuse or other dramatic evidence of something happening. If something does, stop here, disconnect the power and report what you observed.
Collect measurements from the following steps A - H and report what you observe. As before, stop, disconnect power and report observations if anything happens that isn't expected.
These measurements are much more easily done if the black lead of the DMM can be secured to ground, freeing up a hand to operate the switch. eg. clip the black lead to the grounded side of a load resistor. If nothing else is available, inserting the black probe into the grounded mounting hole near the card edge connector and leaving it leaning against the edge may work. Be careful to not dislodge the probe while power is on; you might want to tape it in place. Turn off the power strip if you need to fiddle with this connection.
On/Off in the following refers to the small switch on the test jig attached to the card edge. The power strip can remain on (the behaviour of some of the following measurements is different if the power strip is turned off/on instead of the test jig's switch).
A. Turn off, locate pin 13 of the daughterboard connector (at the CR15 end), then while watching the voltage at pin 13, turn on: the voltage should rise from a low voltage about 0.5V to about 4.8V over a few seconds.
B. Turn off, then while watching the voltage at pin 8 of the daughterboard connector, turn on: the voltage should rise briefly, from near 0 to near 5V, then return to 0. This takes less than a second but should be visible. If it is stuck at 0, double check the interlock switch has been bypassed.
C. Turn off. Carefully (be careful the probe does not slip and cause a short circuit) hold the red probe to the lower end of R30 on the daughterboard (R30 is at the left edge/corner). The voltage should be near 4V. Then while watching the voltage, turn on: the voltage should drop immediately to near 0. If the voltage remains high (around 4 VDC) then the soft-power circuit is suspect.
D. Turn off. Carefully (be careful the probe does not slip and cause a short circuit) hold the red probe to the + (plus) side of C14 on the daughterboard (not far from R30). Then while watching the voltage, turn on: the voltage should rise over a few seconds from near 0 to near 4.8V. If stuck (around 0 VDC), then the brownout circuit is suspect.
E. Turn off, then while watching the voltage at pin 10 of the daughterboard connector, turn on: the voltage should drop from about 2.4V to about 1.4V for a noticeable but brief period (less than a second). If you don't see the brief drop, turn off, switch the DMM to AC Volts and when you turn on again, you should observe the AC voltage briefly rise from 0V to perhaps 1V (the value will depend on the DMM), then return to 0 before you turn off again. If no activity is observed, then Z2 on the daughterboard is suspect. Set the DMM back to DC Volts.
F. Turn off, then while watching the voltage at pin 11 of the daughterboard connector, turn on: the voltage should drop from about 2.4V to about 1.4V for a noticeable but brief period (less than a second). If you don't see the brief drop, turn off, switch the DMM to AC Volts and when you turn on again, you should observe the AC voltage briefly rise from 0V to perhaps 1V (the value will depend on the DMM), then return to 0 before you turn off again. If no activity is observed, then Z2 on the daughterboard is suspect. Set the DMM back to DC Volts.
G. Turn off, locate R7 on the main board. R7 is on ceramic standoffs beside a silvery heatsink plate. One end should measure around 16-18V. While watching the voltage at the other end, turn on, the voltage should rise briefly, from about 1.6V to 5-15V (varies depending on the speed of your DMM), then return to 1.6. If no activity is observed, then Q4 or T5 is suspect.
H. Turn off, locate R5 on the main board. R5 is on ceramic standoffs near the center beside R4. One end should measure around 16-18V. While watching the voltage at the other end, turn on, the voltage should rise briefly, from about 1.6V to 5-15V (varies depending on the speed of your DMM), then return to 1.6. If no activity is observed, then Q3 or T4 is suspect.
Quote from: TorZidan on September 21, 2026, 07:31:39 PMare you a human?
Ah, the eternal question.
Thanks for your kind words; I'm hoping that describing this example of the process will be useful to others someday too, but 'are you not entertained' is sufficient reward.
A computer that can still be repaired at the component level by moderately technical users is, I think, a fortunate anachronism.
Quote from: sigma7 on September 22, 2026, 03:38:33 AMRefer to the drawing, and measure the resistance between each of these pairs (Q1 and Q2 still removed from the circuit):
T4:5 - T4:6
T5:5 - T5:6
In each case, the resistance should be close to 0.0 ohms.
T4:5 - T4:6. in ohms mode 0 ohms
T5:5 - T5:6. in ohms move 0 ohms
Quote from: sigma7 on September 22, 2026, 04:15:38 AMNormally, with Q1 and Q2 out of circuit (either completely, or with the 4 phillips head mounting screws removed such that their cases are disconnected), the main transformer will not receive any switching current.
In this state, the only output voltage will be +5Standby.
With the high power circuitry inactive, we can (hopefully) check some of the control circuitry without having a fault in the high power circuitry blowing the fuse.
Double check that Q1 and Q2 are disconnected (4 screws removed) or completely removed from the circuit board.
Ensure a good fuse is installed.
Connect the test jig load circuit to the card edge, and turn its small switch "off".
Do I connect CR18 again? I would presume so. I also took out the heatsink and screws for T3, and T4. And should the daughter board be placed back in before testing?
Quote from: berskyboy on September 22, 2026, 09:55:59 AMT4:5 - T4:6. in ohms mode 0 ohms
T5:5 - T5:6. in ohms mode 0 ohms
Ok, good.
Quote from: berskyboy on September 22, 2026, 10:00:15 AMDo I connect CR18 again? I would presume so. I also took out the heatsink and screws for T3, and T4. And should the daughter board be placed back in before testing?
You can reconnect CR18 or leave it disconnected at your convenience.
The daughterboard should be in place.
T3 and T4 don't have a heatsink or screws. If you mean Q1 & Q2, at a minimum, the screws should be removed, if the heatsinks are then loose, removing them too is wise.
Quote from: sigma7 on September 22, 2026, 04:15:38 AMNormally, with Q1 and Q2 out of circuit (either completely, or with the 4 phillips head mounting screws removed such that their cases are disconnected), the main transformer will not receive any switching current.
In this state, the only output voltage will be +5Standby.
With the high power circuitry inactive, we can (hopefully) check some of the control circuitry without having a fault in the high power circuitry blowing the fuse.
Double check that Q1 and Q2 are disconnected (4 screws removed) or completely removed from the circuit board.
Ensure a good fuse is installed.
Connect the test jig load circuit to the card edge, and turn its small switch "off".
The small switch should still be in the OFF position, and the power strip will be on. Check the DC and AC voltages from pin 3 of the daughterboard connector to ground. This should be about 16 to 18V DC, and should have an AC voltage of less than 1V; if the DC and AC voltage are in that range, continue with the next step. If not, stop here, remove power, and report what you observed. If the DC voltage is about half or double, investigate whether the 115/230V jumpers are not installed correctly or damaged or not making proper contact. If the DC voltage was zero, check the fuse.
-DC: 17 V
-AC: 0.111 V
-Fuse OK
Remember to set the meter back to DC volts after measuring the AC volts.
Check the DC voltage across R33 (from one end to the other, not to ground)
-161V
& across R2.
-161V
(These are two large resistors beside the large black capacitor C8.) They should be about 150-170 V each (positive or negative, depending on which way you probe them): if so, continue with the next step. If not, then the primary rectifier, line filter, and associated components are suspect - stop here, remove power, and report what you observed.
Check the DC voltage at pin 12 of the daughterboard connector to ground. This should be about 5V:
-4.97V
if so, continue with the next step. If not then Z2 on the daughterboard is suspect - stop here, remove power, and report what you observed.
Make sure the interlock switch has been engaged. Set the small switch (on the test jig connected to the card edge) to the ON position. There should not be any smoke, flashes, odours, blown fuse or other dramatic evidence of something happening. If something does, stop here, disconnect the power and report what you observed.
-ok
Collect measurements from the following steps A - H and report what you observe. As before, stop, disconnect power and report observations if anything happens that isn't expected.
These measurements are much more easily done if the black lead of the DMM can be secured to ground, freeing up a hand to operate the switch. eg. clip the black lead to the grounded side of a load resistor. If nothing else is available, inserting the black probe into the grounded mounting hole near the card edge connector and leaving it leaning against the edge may work. Be careful to not dislodge the probe while power is on; you might want to tape it in place. Turn off the power strip if you need to fiddle with this connection.
On/Off in the following refers to the small switch on the test jig attached to the card edge. The power strip can remain on (the behaviour of some of the following measurements is different if the power strip is turned off/on instead of the test jig's switch).
A. Turn off, locate pin 13 of the daughterboard connector (at the CR15 end), then while watching the voltage at pin 13, turn on: the voltage should rise from a low voltage about 0.5V to about 4.8V over a few seconds.
-0.388V to 4.64V (then stays at 4.6V)
B. Turn off, then while watching the voltage at pin 8 of the daughterboard connector, turn on: the voltage should rise briefly, from near 0 to near 5V, then return to 0. This takes less than a second but should be visible. If it is stuck at 0, double check the interlock switch has been bypassed.
-0.01v to 4.6V then down to 0.025v
C. Turn off. Carefully (be careful the probe does not slip and cause a short circuit) hold the red probe to the lower end of R30 on the daughterboard (R30 is at the left edge/corner). The voltage should be near 4V. Then while watching the voltage, turn on: the voltage should drop immediately to near 0. If the voltage remains high (around 4 VDC) then the soft-power circuit is suspect.
-no 0V, but I might not be putt the probe correctly
D. Turn off. Carefully (be careful the probe does not slip and cause a short circuit) hold the red probe to the + (plus) side of C14 on the daughterboard (not far from R30). Then while watching the voltage, turn on: the voltage should rise over a few seconds from near 0 to near 4.8V. If stuck (around 0 VDC), then the brownout circuit is suspect.
-4.63V
E. Turn off, then while watching the voltage at pin 10 of the daughterboard connector, turn on: the voltage should drop from about 2.4V to about 1.4V for a noticeable but brief period (less than a second). If you don't see the brief drop, turn off, switch the DMM to AC Volts and when you turn on again, you should observe the AC voltage briefly rise from 0V to perhaps 1V (the value will depend on the DMM), then return to 0 before you turn off again. If no activity is observed, then Z2 on the daughterboard is suspect. Set the DMM back to DC Volts.
-goes 2.25v to 1.43v then back to 2.25v
F. Turn off, then while watching the voltage at pin 11 of the daughterboard connector, turn on: the voltage should drop from about 2.4V to about 1.4V for a noticeable but brief period (less than a second). If you don't see the brief drop, turn off, switch the DMM to AC Volts and when you turn on again, you should observe the AC voltage briefly rise from 0V to perhaps 1V (the value will depend on the DMM), then return to 0 before you turn off again. If no activity is observed, then Z2 on the daughterboard is suspect. Set the DMM back to DC Volts.
-2.25v then 1.84v then 2.25v
G. Turn off, locate R7 on the main board. R7 is on ceramic standoffs beside a silvery heatsink plate. One end should measure around 16-18V. While watching the voltage at the other end, turn on, the voltage should rise briefly, from about 1.6V to 5-15V (varies depending on the speed of your DMM), then return to 1.6. If no activity is observed, then Q4 or T5 is suspect.
-1.621v to 11.3V then 1.63V (resistor to ground)
H. Turn off, locate R5 on the main board. R5 is on ceramic standoffs near the center beside R4. One end should measure around 16-18V. While watching the voltage at the other end, turn on, the voltage should rise briefly, from about 1.6V to 5-15V (varies depending on the speed of your DMM), then return to 1.6. If no activity is observed, then Q3 or T4 is suspect.
-1.631v to 9.72V then 1.63V (resistor to ground)
Quote from: berskyboy on September 22, 2026, 02:12:00 PM-1.631v to 9.72V then 1.63V (resistor to ground)
I'm assuming the "-" prefix in these readings doesn't indicate negative voltage... if it does then let me know.
The measurements E-H suggest the SG3524 on the daughterboard is attempting to drive the power circuit, so it is probably good. The other measurements suggest the ancillary circuitry is also working.
We haven't thoroughly checked the secondary side of the PSU, but since you have replaced the output capacitors, and we confirmed the rectifier diodes look like diodes, there is a good chance it is ok.
I suspect we found and corrected the original fault (a broken solder joint at the trimmer potentiometer R11), and the fault that caused Q1 & Q2 to fail, solder bridge(s).
So I suspect that replacing Q1 & Q2 (and ensuring there are no solder bridges remaining) is likely to be sufficient to repair the fault that blows the fuse.
The original 2N6308 transistors are no longer made, so finding a substitute is the usual option, although one could look for old-stock originals on eBay etc.
A few posts back, you referenced a Newark/Element14 cart with BUX48A transistors in it. Did you find references that indicate this is a suitable substitute?
Does anyone else have a recommendation for a currently available 2N6308 substitute that works in this PSU?
Quote from: sigma7 on September 22, 2026, 02:36:13 PMI'm assuming the "-" prefix in these readings doesn't indicate negative voltage... if it does then let me know.
that denoted a measurement. Sorry I wanted to separate it.
But what about this value?:
C. Turn off. Carefully (be careful the probe does not slip and cause a short circuit) hold the red probe to the lower end of R30 on the daughterboard (R30 is at the left edge/corner). The voltage should be near 4V. Then while watching the voltage, turn on: the voltage should drop immediately to near 0. If the voltage remains high (around 4 VDC) then the soft-power circuit is suspect.
-no 0V, but I might not be putt the probe correctly
Quote from: sigma7 on September 22, 2026, 02:36:13 PMSo I suspect that replacing Q1 & Q2 (and ensuring there are no solder bridges remaining) is likely to be sufficient to repair the fault that blows the fuse.
The original 2N6308 transistors are no longer made, so finding a substitute is the usual option, although one could look for old-stock originals on eBay etc.
A few posts back, you referenced a Newark/Element14 cart with BUX48A transistors in it. Did you find references that indicate this is a suitable substitute?
Does anyone else have a recommendation for a currently available 2N6308 substitute that works in this PSU?
This is what I found.
BUX48A
TRANS, BIPOLAR, NPN, 450V, 15A, TO-3
https://canada.newark.com/multicomp-pro/bux48a/trans-bipolar-npn-450v-15a-to/dp/23AJ5969
from AI or google:
Yes, the BUX48A can replace the 2N6308 in most high-voltage power supply, inverter, and switching applications. It matches the package type, exceeds all critical maximum voltage and current limits, and provides equivalent or better switching speeds. Solitron Devices, Inc. +3
https://solitrondevices.com/datasheets/2n6306_8-ds.pdf
Quote from: berskyboy on September 22, 2026, 02:54:44 PMBut what about this value?:
C. ..
-no 0V, but I might not be putt the probe correctly
The fact that E - H show the SG3524 attempting to run indicates the soft-power circuit is working, so I think it doesn't matter if either you weren't able to probe it or my predictions were incorrect.
Quote from: berskyboy on September 22, 2026, 03:02:26 PMThis is what I found.
from AI or google:
Yes, the BUX48A can replace the 2N6308 in most high-voltage power supply
Neither AI nor google have any direct knowledge, they've only collected bits of information from elsewhere, and sometimes combine them incorrectly, so they can't be considered an authoritative or reliable source. eg. AI was previously telling you to replace a part that isn't there.
So I'm hoping there is a better source, if not, we will compare specifications in an attempt to confirm the suggestion is reasonable.
I'm found and bought from this site the 2N6308
https://www.tedss.com/2028023156
Quote from: berskyboy on September 22, 2026, 09:38:40 PMfound and bought from this site the 2N6308
Good choice!
It looks like there are very few TO-3 transistor packages still being made. The plastic case alternative will not be trivial to retrofit in the DataPower PSU.
Quote from: berskyboy on September 22, 2026, 09:38:40 PMfound and bought
While you're waiting for those to arrive, anticipate if you will need to procure some additional items to install them.
If you can remove the mica insulators from the old transistors without breaking them, you can re-use them.
In addition, thermally conductive grease/compound is needed with mica insulators. In a pinch, if the old parts have plenty and it is clean, you can re-use the grease, but cleaning it off and using new grease can help avoid issues. The fancy heatsink compound used for computer CPUs/GPUs is the same type of material (but more expensive) and may be easier to get locally, or you may already have some.
Watch some videos to see how much grease to use... the final layers should be very thin (eg. almost translucent), too much will make thermal transfer worse. You may need slightly more for broad contact if the heatsink surface isn't very flat. Keep grease away from where the leads enter the transistor case.
There is also the option of replacing the grease and mica with a TO-3 shape silicone insulator pad. I've not read confirmations that this works ok in this PSU, but I expect so. The silicone pad option does not need grease; clean off all the old grease if switching to a silicone pad.
If any of the TO-3 mounting screws were difficult to remove, the solder joint between the threaded mounting post and the circuit board may have broken. This is best resoldered without the screw and transistor in place. On the bottom of the main board, carefully check for cracks in the solder around the outside of the threaded mounting posts and resolder if the joint is suspect. Avoid putting more solder in the hole (and remove solder in the hole if possible).
Important: When re-installing the TO-3 transistors, you must complete the physical mounting before soldering the leads. ie. clean and grease the mating surfaces, assemble, and fully tighten the phillips head screws before soldering anything. Soldering too soon introduces mechanical stresses that can damage the transistor and circuit board.
The DataPower PSU was originally wave soldered after the TO-3 transistors were installed. As a result, the transistor mounting screw holes have solder in them. Check carefully that the transistors are rigidly clamped down against the heatsink; if not, the solder in the screw holes may be preventing full engagement of the screws. If you have appropriate equipment, you may be able to remove the solder from the screw holes, or you can use a 6-32 tap or something similar to clear solder from inside the threaded hole. You do not need to re-solder the mounting screws once re-installed.
Once the screws are tightened, check that the insulator has not been compromised by measuring the resistance between the heatsink and the case of the transistor. It should have a very high resistance. The black coating on the heatsink is non-conductive, so you'll need to pierce it, scrape a bit off, or find a spot that isn't black. Measure the resistance from one spot to another on the heatsink to confirm you've established good contact.
Double check that all other components (such as CR18) have been re-installed to return the PSU to the fully assembled state.
Quote from: sigma7 on September 23, 2026, 03:25:19 PMWhile you're waiting for those to arrive, anticipate if you will need to procure some additional items to install them.
If you can remove the mica insulators from the old transistors without breaking them, you can re-use them.
I think I can use them and wipe them off
Quote from: sigma7 on September 23, 2026, 03:25:19 PMIn addition, thermally conductive grease/compound is needed with mica insulators.
I have ordered this.
https://canada.newark.com/wakefield-thermal/120-sa/thermal-grease-compound-packet/dp/00Z1244?CMP=e-email-sys-shipping-GLB-Product
Quote from: sigma7 on September 23, 2026, 03:25:19 PMWatch some videos to see how much grease to use... the final layers should be very thin (eg. almost translucent), too much will make thermal transfer worse. You may need slightly more for broad contact if the heatsink surface isn't very flat. Keep grease away from where the leads enter the transistor case.
would this be a good video for that?
https://www.youtube.com/watch?v=ufTi-lH4nw4
Quote from: berskyboy on September 23, 2026, 07:18:51 PMQuote from: sigma7 on September 23, 2026, 03:25:19 PMWatch some videos to see how much grease to use... the final layers should be very thin (eg. almost translucent), too much will make thermal transfer worse. You may need slightly more for broad contact if the heatsink surface isn't very flat. Keep grease away from where the leads enter the transistor case.
would this be a good video for that?
https://www.youtube.com/watch?v=ufTi-lH4nw4
No.
Edit to add some details:
To be fair, if it is done that way, it might be fine, and probably is in many cases, especially if you are doing service for a fee and the time consumed to do the job is a concern. But I think the video is probably not considered a demonstration of ideal technique by many, and we can hope the Lisa PSU might be useful for another 40+ years, so taking the time to do a good job is warranted.
It is a good point that if the old material is dried out, re-using it would be a last resort.
My criticisms of the approach shown:
1. Not keeping the transistor leads clean: Apparently the silicone oil can migrate past the glass insulator around a lead and contaminate the transistor inside the case. Supposedly this takes a long time, so probably only an issue for ultimate longevity. I don't know what consequences there are to contaminating the inside, perhaps not relevant here to a switching/power transistor. Regardless, aside from saving the time it takes to be careful, there isn't any advantage to putting grease on the lead.
2. Using a power tool to attach the hardware: the time saved over dozens of repairs is completely wiped out when you have to fix a stripped/damaged tapped hole in a heatsink or threaded standoff. There are specific circumstances where a power tool might be used, but it should not be implied as standard procedure.
3. Not starting with clean surfaces: the best thermal contact is when the surfaces are as close together as possible. This can easily be compromised if the surfaces are not clean.
4. Using more grease than necessary: As above, the best thermal contact is when the surfaces are as close together as possible. The grease is there only to fill the gaps (since air is a good insulator), so there should be as little as possible. This is not a case of "the bigger the gob, the better the job" as AvE sometimes says tongue-in-cheek when tearing down equipment. (If you're not familiar with AvE (https://www.youtube.com/@arduinoversusevil2025/videos), you might find him amusing, although some of the vernacular may be a bit opaque if you're not Canadian.)
Not specific to the video is checking the quality of the mating surfaces. Quality-control cutbacks are sometimes revealed as non-flat surfaces, raised dings, as well as burrs around holes. These prevent close contact and result in poor heat transfer (which results in failed transistors as they overheat). At minimum, check for and remove burrs around holes in heatsinks.
I may add more thoughts/opinions later.
Quote from: sigma7 on September 23, 2026, 07:36:30 PMTo be fair, if it is done that way, it might be fine, and probably is in many cases, especially if you are doing service for a fee and the time consumed to do the job is a concern. But I think the video is probably not considered a demonstration of ideal technique by many, and we can hope the Lisa PSU might be useful for another 40+ years, so taking the time to do a good job is warranted.
Good point. 40+ years, yes a definite goal to aspire to. I'm in your debt for all the help you have shown me, and even these tips for success. (ie Goal of 40+ years), which is "inline" with how they designed and made the Apple Lisa (from my exposure it looks like they didn't cut corners and did the best job to last 40+ years).
I will do more research on the topic and find other videos.
Quote from: berskyboy on September 23, 2026, 11:49:43 PMdid the best job to last 40+ years
except for the I/O board battery though :)
(Could they have known?)
Quote from: stepleton on September 24, 2026, 03:28:34 AMQuote from: berskyboy on September 23, 2026, 11:49:43 PMdid the best job to last 40+ years
except for the I/O board battery though :)
(Could they have known?)
I think someone expected as much - witness the 16 year range of the RTC. :P
Hi @sigma7
I will receive the Q1 and Q2 parts in the mail on Thursday. In the meantime. I did purchase an Apple Lisa Video Board, and took an initial look at the board for the condition of the components, is there some bench tests I can run on that board? If there is a link to an existing POST on this you can link to that one.
Quote from: berskyboy on September 27, 2026, 05:25:49 PMI will receive the Q1 and Q2 parts in the mail on Thursday.
Excellent. Before you install them, you should check them with the diode test to make sure they look plausibly like transistors. Measure all 6 permutations of red & black to the 3 connections.
QuoteI did purchase an Apple Lisa Video Board, and took an initial look at the board for the condition of the components, is there some bench tests I can run on that board? If there is a link to an existing POST on this you can link to that one.
I'm not aware of anyone posting techniques for testing the Video board out of the Lisa. If you have a 30-36V power source, you could check the 7824 regulator (which sometimes fails), but most further testing requires the video signals from the CPU board.
I think the safest approach is to assume it works and then troubleshoot any symptoms.
If you see some scorching or distorted components, you could post pics.
Hi, good morning,
So I put the Apple Lisa Video card in. I put the Yoke pins into the Tube carefully making sure it lined up and the pins were straight. I put P1 (Red and White) and P2 (Green and Yellow)
https://www.dropbox.com/scl/fi/a6ufm4ge7x852k15bavbi/P1-and-P2-Lisa-Video-Board.heic?rlkey=bcjfbaaf32te7pq0tfvz5lrbd&st=22w2u3qi&dl=0
1. I also wanted to know how to ground the white wire,
2. The small green and white wire seem to be grounds?
https://www.dropbox.com/scl/fi/qae6ed3mu7onn45dfcffi/Ground-plus-green-and-yellow.heic?rlkey=upumms96ri0otqhf03pn03d0e&st=nnic0692&dl=0
Resource:
Apple Lisa Manuel
https://media.512pixels.net/wp-content/uploads/2025/05/Lisa-DIY-Guide.pdf. (page 47-48)
Quote from: berskyboy on September 28, 2026, 11:53:07 AM1. I also wanted to know how to ground the white wire
2. The small green and white wire seem to be grounds?
The white wire from the tube socket does go to the spade connector on the metal chassis as in your picture.
The two thin green and white wires go to the front panel safety interlock switch (near the bottom left corner of the CRT). Many people just disable the switch, so that may be why your wires are cut.
Quote from: sigma7 on September 28, 2026, 12:47:39 PMThe white wire from the tube socket does go to the spade connector on the metal chassis as in your picture.
so the white wire goes to the read circle?
https://www.dropbox.com/scl/fi/lgmzu07e6eve7dusb7v0t/White-Wire-goes-to-Red-Circle.jpeg?rlkey=0wxa7j8uncfm485z00tj1p9ht&st=t4yvxw57&dl=0
Also, do I need to worry about this? (I asked AI about the picture)
⚠️ Crucial Step: Where is the CRT Aquadag Ground Strap?
Because that white wire goes to the neck socket, you must verify the main CRT static grounding strap is still present.
- Look for a bare, uninsulated braided metal wire or a thin tension spring stretched tightly across the black matte coating (aquadag) on the wide, curved part of the glass funnel.
- This braided strap must connect to a grounding point on one of the four metal corner mounting ears of the CRT frame.
Double-check that the bare metal grounding strap is contacting the black glass coating before you reinstall the main plastic outer housing.
CRT televisions and monitors can cause serious injury or death, even when unplugged for days, weeks, or months. Read and follow all precautions before opening any CRT device.
LETHAL HIGH VOLTAGE
The anode (high-voltage) circuit can hold 20,000-30,000+ volts on the tube's second anode, the suction-cup connector on the glass.
Capacitors, including the tube itself, can retain a dangerous charge long after power is removed.
Flyback transformers and the associated circuitry can also deliver painful or dangerous shocks.
IMPLOSION HAZARD
The glass envelope is under vacuum and can implode violently if cracked, scratched, or struck.
Flying glass can cause severe lacerations and eye injuries.
Never carry a tube by its neck. Never apply pressure to the neck or the neck board.
Wear safety glasses or a face shield at all times.
BEFORE YOU BEGIN
Unplug the device from mains power.
Work only if you are trained or experienced with high-voltage electronics. If you are not, do not open the case.
Never work alone. Have someone nearby who can call for help and knows CPR.
Keep one hand in your pocket or behind your back when probing live circuits, to avoid a path across your chest and heart.
Remove jewelry and metal accessories.
Work on a dry, non-conductive surface. Keep liquids away from the work area.
DISCHARGING
Discharge the anode only with a properly insulated, high-voltage discharge tool and a known-good ground connection, following the correct procedure for your specific device.
Never use a bare screwdriver or improvised tool. This can damage components and injure you.
Do not assume the tube is discharged. Verify with an appropriate high-voltage probe.
Recharging can occur after discharge (dielectric absorption), so re-check before touching.
Quote from: TorZidan on September 28, 2026, 02:24:38 PMCRT televisions and monitors can cause serious injury or death, even when unplugged for days, weeks, or months. Read and follow all precautions before opening any CRT device.
hi TorZidan, yup it came unplugged and the CRT was even upside down. I'm still working bench testing the PSU. So no power as of yet. And could have been for a decade or so :), but yes I made a screwdriver with an alligator clip and have discharged few vintage CRTs (NeXT Monitor, Mac SE).
My question was regarding what AI said, and I'm wondering if I'm missing any parts.
https://youtube.com/shorts/K4iUFtFl23A
Quote from: berskyboy on September 28, 2026, 04:05:19 PMI made a screwdriver with an alligator clip and have discharged few vintage CRTs (NeXT Monitor, Mac SE).
For the benefit of others, that would be a "sufficiently insulated" screwdriver, as a few KV will go through the otherwise insulating handle of many screwdrivers. This kind of non-obvious detail is why the warning specifies "Work only if you are trained or experienced with high-voltage electronics." Working around the CRT is dangerous: proceed at your own risk!
Also, the alligator clip is typically wired through a high value resistor so the current surge is limited.
Note that the high voltage of the CRT stinger will damage/destroy a DMM unless a working high voltage probe is used properly. According to the video board schematic, the Lisa CRT HV is 13KV (and may be higher if there is a fault in the circuitry). DMMs are typically limited to 1KV, some much less.
Quotethe CRT was even upside down.
An upside down CRT might be intended as a warning sign. You've found quite a project!
QuoteMy question was regarding what AI said
It is good you asked. It looks like AI has led you astray a couple of times already, so we should all take its responses as "concepts to investigate" rather than "directions to follow" as worded.
The black coating/paint on the CRT should have a low resistance to the chassis. This connection is made (on some Lisa CRTs at least) via a flat copper spring loop at one side of the CRT. (Different from what AI said it would be)
If the spring isn't there, and you don't have a low resistance from the chassis to the black conductive dag coating, then indeed some other connection is needed.
Quoteand I'm wondering if I'm missing any parts
In your video, I see a Widget hard drive (above the floppy drive), which if still working, you probably don't want to use since a modern emulator will give better performance, be more convenient, and preserve what life is left (if any) in the Widget.
The Widget does not have a power or data cable connected. What are the cables in that area that are not connected?
Given the other oddities, I wonder if you have a full wiring harness... check if there is a card edge connector for the PSU to plug into, another for the motherboard to plug into, and another for the video card to plug into. There should also be a connector plugged into the flyback transformer, the other ends of the thin green and white wires, and wires going to the speaker behind the front panel safety interlock switch. And finally, another (non-ribbon cable) connector in the drive cage area (there are two different types, depending on the type of wiring harness).
You may/probably need to clean and re-lubricate the 400K Sony drive if you wish to use it.
Quote from: sigma7 on September 28, 2026, 04:57:24 PMQuote from: berskyboy on September 28, 2026, 04:05:19 PMI made a screwdriver with an alligator clip and have discharged few vintage CRTs (NeXT Monitor, Mac SE).
It is good you asked. It looks like AI has led you astray a couple of times already, so we should all take its responses as "concepts to investigate" rather than "directions to follow" as worded.
The black coating/paint on the CRT should have a low resistance to the chassis. This connection is made (on some CRTs at least) via a copper wide spring loop at one side of the CRT. (Different from what AI said it would be)
If the spring isn't there, and you don't have a low resistance from the chassis to the dag coating, then indeed some other connection is needed.
So I'm not 100% certain what I'm looking for here, here's another look at the CRT
https://www.dropbox.com/scl/fi/e73juylm4yrwcdzws1lj6/Lisa-CRT.HEIC?rlkey=2nnsz4katm1txogbylds112kz&st=1lzh311w&dl=0
And I did created a 60 pin cable after watching Adrian's YouTube Video.
https://www.dropbox.com/scl/fi/fss0cuwubwnschhmr5564/Recreated-Ribbon.HEIC?rlkey=f5fkgyglxtyuvj0dl7lh3i2bn&st=ohtg7269&dl=0
Quote from: berskyboy on September 28, 2026, 05:36:42 PMQuote from: sigma7 on September 28, 2026, 04:57:24 PMThe black coating/paint on the CRT should have a low resistance to the chassis. This connection is made (on some CRTs at least) via a copper wide spring loop at one side of the CRT. (Different from what AI said it would be)
So I'm not 100% certain what I'm looking for here
1. Use the DMM to measure the resistance from the black paint (on the CRT) to the silvery metal chassis.
2. Look around the perimeter of the CRT for a copper coloured flat spring that goes between the CRT and the silvery metal chassis.
Quote from: TorZidan on September 28, 2026, 02:24:38 PMCRT televisions and monitors can cause serious injury or death
Thanks for posting this warning; I'll repost it to the Troubleshooting area.
Quote from: sigma7 on September 28, 2026, 05:51:19 PM1. Use the DMM to measure the resistance from the black paint (on the CRT) to the silvery metal chassis.
2. Look around the perimeter of the CRT for a copper coloured flat spring that goes between the CRT and the silvery metal chassis.
Here's a video with my measurements using DMM
https://www.youtube.com/shorts/ixwfd6GJof0
Quote from: berskyboy on September 28, 2026, 06:43:04 PMQuote from: sigma7 on September 28, 2026, 05:51:19 PM1. Use the DMM to measure the resistance from the black paint (on the CRT) to the silvery metal chassis.
2. Look around the perimeter of the CRT for a copper coloured flat spring that goes between the CRT and the silvery metal chassis.
Here's a video with my measurements using DMM
A couple of hundred ohms seems plausible, depending on where you probe the conductive coating.
So that may mean the copper flat spring is in place somewhere, possible at the right side where the chassis is very close to the tube. If you can find it, please post a picture for reference by future troubleshooters.
Quote from: sigma7 on September 28, 2026, 04:57:24 PMAn upside down CRT might be intended as a warning sign. You've found quite a project!
Fun fact: rotating the CRT 180 degrees was a (recommended) regular maintenance item for Tektronix 4050-series vector storage display computers, intended to preserve the life of the storage CRT. I don't think many people actually did it, and for the 4054 and 4054A, you probably would have wanted an engine hoist to help out with the job.
Quote from: sigma7 on September 23, 2026, 07:36:30 PM(If you're not familiar with AvE (https://www.youtube.com/@arduinoversusevil2025/videos), you might find him amusing, although some of the vernacular may be a bit opaque if you're not Canadian.)
By the way. This guy is hilarious!!!
Quote from: sigma7 on September 27, 2026, 06:12:25 PMExcellent. Before you install them, you should check them with the diode test to make sure they look plausibly like transistors. Measure all 6 permutations of red & black to the 3 connections.
I just got the Q1 and Q2 transistors.
Measurements as follows (I bought 4, 2 spares)
DIODE TEST
Red to Black 1, 2 3, 4
Lead 1 to Lead 2 0.537, 0.536 0.530, 0.540
Lead 2 to Lead 1 OL, OL OL, OL
Lead 1 to case 0.467, 0.471 0.471, 0.462
case to Lead 1 OL, OL OL, OL
Lead 2 to case OL, OL OL, OL
case to Lead 2 OL, OL OL, OL
I will have time to put them in the PSU tomorrow.
Quote from: berskyboy on September 30, 2026, 06:47:32 PMI just got the Q1 and Q2 transistors.
Measurements as follows (I bought 4, 2 spares)
...
Awesome, they look like NPN transistors!
If you have a sensitive scale, then before you install the transistors, you might consider weighing the ones that you have, old and new.
Counterfeit parts are more and more of a problem these days, and I've seen a post or two on other forums complaining of replacement power transistors that weren't what was advertised. When one poster cut open their new transistors' TO-3 cans, what they found was a substantially smaller and flimsier chunk of silicon inside. Now, as manufacturing processes improve, you might expect the silicon to shrink somewhat over a component's production lifetime, but I assume that for a power transistor this is only to a point. A radical die shrink probably isn't so realistic, as I assume you must have some amount of silicon to conduct current.
For the purposes of this project, you might use this information as follows:
- If the PSU still doesn't work (or soon breaks again) and the new transistors were a lot lighter, you might consider the possibility that you got phony parts and try sourcing new replacements from somewhere else.
- Otherwise, if there are problems and the new transistors were roughly the same weight, you might suspect that there is still another fault elsewhere in the PSU.
Specialised equipment like a curve tracer could tell you more about whether the new transistors were likely to behave like the older ones, but I suspect you don't have one of those. (I wish I did!) Lacking that, weight is one of the few comparative measurements that's easy to take.
Quote from: stepleton on October 01, 2026, 03:55:35 AMIf you have a sensitive scale, then before you install the transistors, you might consider weighing the ones that you have, old and new.
thanks for the tip, yup it's 10.8g same as the original. I weighted all of them. So this distributor is reputable.
Quote from: sigma7 on September 27, 2026, 06:12:25 PMExcellent. Before you install them, you should check them with the diode test to make sure they look plausibly like transistors. Measure all 6 permutations of red & black to the 3 connections.
I've tested Q1 and Q2 on the board
{7-8, 10-11} 0.00 Q2, Q1 e-b (in parallel with pulse transformer) Ov, 0v. [0, 0 ]
{8-7, 11-10} 0.00 Q2, Q1 b-e (in parallel with pulse transformer) 0v, 0v. [0, 0 ]
{7-9, 10-12} 0.46 Q2, Q1 e-c [ 0.468, 0.455]
{9-7, 12-10} inf Q2, Q1 c-e [OL,OL]
{8-9, 11-12} 0.46 Q2, Q1 b-c [0.468, 0.463]
{9-8, 12-11} inf Q2, Q1 c-b [OL, OL]
So I put the testing edge connector and measured around to 5V getting 5V then drops slowly (not as quick as before all the Q1 and Q2 issue). The 12V rail 11.5v then dropping slowly.
Here's the two videos
5V Rail
https://www.youtube.com/shorts/F0PeQeJKY8M
12V Rail
https://www.youtube.com/shorts/ScXZ-lT0yqA
Just for a kick this is what Gemini AI said. (I know you want to keep AI honest) :)
Your videos provide excellent context, showing the voltage initially jumping up to 5.4V on the 5V rail (0:07) and around 11.5V–11.8V on the 12V rail, followed by a slow, gradual decline (0:07).
The fact that the voltage is dropping slowly (and much slower than it did before you resolved the Q1 and Q2 transistor issues) is a massive clue. This behavior points directly to how the Apple Lisa power supply unit (PSU) interacts with a computer that is stripped down on a test bench.
🔍 Why the Voltages are Slowly Dropping
This slow drop is typically caused by two specific hardware behaviors:
1. Lack of a "Minimum Load" (The Most Likely Culprit)
The Lisa's power supply is a switching power supply.
• Switching power supplies require a minimum electrical current draw (a "load") to stay active and regulate their output.
• If you are testing with only the video board connected—or with the main logic board, card cage, and mechanical Twiggy drives removed—the PSU does not sense enough current draw.
• The Result: The PSU triggers its internal over-voltage or under-load protection and shuts down. The "slow drop" you see on your DMM is actually the large filter capacitors inside the power supply slowly draining their stored energy because nothing is consuming the power (0:07).
Quote from: berskyboy on October 01, 2026, 12:24:20 PMJust for a kick this is what Gemini AI said. (I know you want to keep AI honest) :)
filter capacitors inside the power supply slowly draining their stored energy because nothing is consuming the power (0:07).
This might be a useful point. See if the voltage measured at the load resistors behaves in the same way (test with red and black at the two ends of one resistor, then again with the other resistor).
Quote from: sigma7 on October 01, 2026, 02:06:15 PMThis might be a useful point. See if the voltage measured at the load resistors behaves in the same way (test with red and black at the two ends of one resistor, then again with the other resistor).
I re-seated the edge connector, and put alcohol and tested again. Success 5.37V and 12.49V and it's NOT dropping!
https://www.youtube.com/shorts/Ptwl7Cb_I84
Quote from: berskyboy on October 01, 2026, 03:21:14 PMSuccess 5.5V and 12.5V and it's NOT dropping!
Yes, it looks like it is now working... congrats.
To finish:
Adjust R11 so that +5 is between 4.9 and 5.1. It may need to be adjusted again once you measure it in the fully assembled Lisa.
Check the +33, -12 and -5V outputs.
Consider adding a small low speed fan to enhance longevity.
Quote from: sigma7 on October 01, 2026, 03:39:09 PMTo finish:
Adjust R11 so that +5 is between 4.9 and 5.1. It may need to be adjusted again once you measure it in the fully assembled Lisa.
Check the +33, -12 and -5V outputs.
Sounds good will adjust R11, do I need to touch R26?
And how do I check +33V output, would that be while placed in the Lisa?
Quote from: berskyboy on October 01, 2026, 03:52:41 PMdo I need to touch R26?
And how do I check +33V output
I don't think you need to adjust R26.
If you're going to use a real Widget (the only device which monitors the Power Fail signal AFAIK), then you might need to adjust R26. Perhaps someone else already has a procedure for setting it without a variac?
Check +33, -12 and -5 (those are negative signs) with the same test jig setup you just used to check +12 and +5... ie. don't change anything, just move the red probe.
Quote from: sigma7 on October 01, 2026, 04:11:46 PMheck +33, -12 and -5 (those are negative signs) with the same test jig setup you just used to check +12 and +5... ie. don't change anything, just move the red probe.
it measures -5V when red is on ground on the 5V rail and -11.62V on the 12V rail. Where is the 33+V test?
Quote from: berskyboy on October 01, 2026, 04:17:02 PMWhere is the 33+V test?
Pin "D" on the card edge connector. If you can't get to the bottom for some reason, you could measure something closely related at L5 or the top lead of CR22.
With the card edge connector test jig, pin "D" is readily accessible.
Quote from: berskyboy on October 01, 2026, 04:17:02 PMQuote from: sigma7 on October 01, 2026, 04:11:46 PMheck +33, -12 and -5 (those are negative signs) with the same test jig setup you just used to check +12 and +5... ie. don't change anything, just move the red probe.
it measures -5V when red is on ground on the 5V rail and -11.62V on the 12V rail. Where is the 33+V test?
With black on ground, and red to the -5 rail the meter should read -5V, and with red to the -12 rail, it should read around -12V.
71.2V, that and measured at CR22 also
https://www.youtube.com/shorts/aSk2IGHACGA
Quote from: berskyboy on October 01, 2026, 04:32:49 PM71.2V, that and measured at CR22 also
https://www.youtube.com/shorts/aSk2IGHACGA
Turn it off... the capacitor is rated for 50V.
I suppose that means you need a load on +33V... don't turn it on again until you have one attached.
Since it appears the PSU is working now, if you don't have anything suitable to use as a +33V load, I'd put the PSU in the Lisa and check -5 and -12 on the I/O Board. If the video works fine, then +33 is ok.
would this be the correct on to buy?
https://www.amazon.ca/cart?ref_=ox_ewc_ret_gtc_dsk_ca
from your diagram you have: three 910-ohm, 2-watt resistors side-by-side in parallel
Quote from: sigma7 on October 01, 2026, 04:36:09 PMurn it off... the capacitor is rated for 50V.
I suppose that means you need a load on +33V... don't turn it on again until you have one attached.
Since it appears the PSU is working now, if you don't have anything suitable to use as a +33V load, I'd put the PSU in the Lisa and check -5 and -12 on the I/O Board. If the video works fine, then +33 is ok.
Rats... so is there any test (or re-test) I can do to see what part I need to replace. LOL. Sighh... You mentioned the 50V capacitor maybe I can start there?
EDIT: I took out the 50V capacitor and it measures 0.932mf, so that means it might have blow?
Quote from: berskyboy on October 01, 2026, 05:20:25 PMQuote from: sigma7 on October 01, 2026, 04:36:09 PMurn it off... the capacitor is rated for 50V.
I suppose that means you need a load on +33V... don't turn it on again until you have one attached.
Since it appears the PSU is working now, if you don't have anything suitable to use as a +33V load, I'd put the PSU in the Lisa and check -5 and -12 on the I/O Board. If the video works fine, then +33 is ok.
Rats... so is there any test (or re-test) I can do to see what part I need to replace. LOL. Sighh... You mentioned the 50V capacitor maybe I can start there?
As far as I can see, no damage occurred, so no parts to replace. The only susceptible one was the cap rated at 50V, C25 while being subject to ~71V. Look it over carefully to see if it has swollen at all. If the video is wonky, then you might suspect the +33V filter cap.
If ordering parts you could get a spare for C25 1000uF @
50V 100V. Or perhaps the one you previously removed when re-capping is still good... (does your DMM measure capacitance?).
If you want to keep going on testing the PSU out of the Lisa, then add a +33V load to your card edge test jig.
The +33 output is rated around 0.6A.
To load it at half the rating, you'd want to draw 0.3A, which means using a 110 ohm resistor dissipating 10W.
Or you could use the three 910 ohm resistors in parallel, making a load of 303 ohms drawing 0.11A at 3.6W (1.2W each).
I'm thinking I'll replace C25 with 1000uF @ 100V in the future. If the Lisa is powered up with no video card installed, there will be no load on +33V, so this may save the PSU.
Quote from: sigma7 on October 01, 2026, 05:49:17 PMC25 with 1000uF @ 100V
I think so: https://www.amazon.ca/dp/B08MTTX66X?ref_=ppx_hzsearch_conn_dt_b_fed_asin_title_1&th=1
AstroAI Digital Clamp Meter Multimeter, TRMS Tester with NCV, 2000 Counts
Measures AC Amp, AC/DC Volt, Resistance, Capacitance, Continuity, Diode, Live Wire Test, Flashlight, LCD Backlight
when I tested CR22 I must have touched both leads? There were sparks. But I correctly did measured 71V after that and the 5V and 12V after that, so I didn't think it damaged anything. But my testing board did become very hot, the resisters.
I forgot I do have those car lights I could add to my testing board. I have 910 ohm resistors coming this morning.
https://www.amazon.ca/dp/B0G2B517KW?ref=ppx_yo2ov_dt_b_fed_asin_title&th=1
I have taken out the 1000uF 50V capacitor and tried measuring it. I have a 1000uf 50V coming this morning, and just ordered a 1000uf 100V for today also.
Morning,
I re-measured all the previous measurements:
Diodes Fwd, Rev Description Final Test
{AA, AB} 0.46, inf CR18, CR19 AA: 0.443,OL AB: 0.447, OL
{BA, BB} 0.13, inf CR18, CR19 BA: 0.130, climbing BB: 0.129, climbing
{CA, CB, CC, CD} 0.5, inf CR1, CR2, CR3, CR4 CA: 0.471, OL CB: 0.478, OL CC: 0.474, OL CD: 0.468, OL
{DA, DB} 0.30, 0.37 CR25, CR23 DA: 0.261, 0.275 DB: 0.265, 0.275
{EA, EB} 0.38, inf CR26, CR24 EA: 0.388, climbing EB: 0.387, climbing
{FA, FB} 0.41, inf CR22, CR21 FA: 0.392, OL FB: 0.391, OL
.
Transistors
Red-Blk Description
{1-2, 4-5} 1.25 Q4, Q3 c-b 0.749, 0.747
{2-1, 5-4} 0.62 Q4, Q3 b-c 0.575, 0.570
{1-3, 4-6} 0.70 Q4, Q3 c-e 0.666, 0.686
{3-1, 6-4} 1.89 Q4, Q3 e-c 1.613, 1.615
{2-3. 5-6} 0.64 Q4, Q3 b-e 0.618, 0.620
{3-2, 6-5} inf Q4, Q3 e-b 1.622, 1.622
{7-8, 10-11} 0.00 Q2, Q1 e-b (in parallel with pulse transformer) 0, 0
{8-7, 11-10} 0.00 Q2, Q1 b-e (in parallel with pulse transformer) 0, 0
{7-9, 10-12} 0.46 Q2, Q1 e-c 0.445, 0.442
{9-7, 12-10} inf Q2, Q1 c-e OL, OL
{8-9, 11-12} 0.46 Q2, Q1 b-c 0.445, 0.442
{9-8, 12-11} inf Q2, Q1 c-b OL, OL
all that seems to check out. I replaced the 50V Cap, the PSU show no voltage on either 5V or 12V rail. Maybe my resistors or something on my test board failed?
EDIT: {3-2, 6-5} inf Q4, Q3 e-b 1.622, 1.622
I think 3-2, 6-5 should be inf? like what you mentioned? But they are 1.622
I will add the 33V load on the my test board today too, when the resistors come
Quote from: berskyboy on Yesterday at 04:28:02 AMQuote from: sigma7 on October 01, 2026, 05:49:17 PMC25 with 1000uF @ 100V
AstroAI Digital Clamp Meter Multimeter, TRMS Tester with NCV, 2000 Counts
Measures ... Capacitance ...
To measure capacitance, you'll need to remove a capacitor from the circuit. Try testing the ones you removed early on to get the hang of it. Measuring capacitance with a DMM doesn't give you all the measurable health information for the capacitor, but it is much better than nothing.
Quotewhen I tested CR22 I must have touched both leads? There were sparks.
A probe slipping and causing a short circuit can quickly damage a lot of components, especially in a high power circuit. Presumably the spark was between the cathodes of CR22 and CR23, which would have bridged the 33V rail to the 12V transformer winding. If it was brief, then I think probably no damage; for a longer period it may damage C26 which is rated for 16V. If you can figure out exactly where the spark/short occurred, that could be helpful. In any case, I would proceed assuming no damage and come back to this if necessary.
Quotemy testing board did become very hot, the resisters.
The resistors will get hot if the PSU is operating for more than a moment... they are effectively heaters.
Quote from: berskyboy on Yesterday at 10:28:14 AMI re-measured all the previous measurements:
EDIT: {3-2, 6-5} inf Q4, Q3 e-b 1.622, 1.622
I think 3-2, 6-5 should be inf? like what you mentioned? But they are 1.622
The Q4, Q3 e-b measurement is different depending on whether the daughterboard is installed or not. I don't think there is a problem there.
QuoteI replaced the 50V Cap, the PSU show no voltage on either 5V or 12V rail. Maybe my resistors or something on my test board failed?
I will add the 33V load on the my test board today too, when the resistors come
The resistors are very unlikely to fail unless you leave it running for a long time and they overheat.
Check the fuse, but
don't turn it on until you have the +33 load installed.
Quote from: sigma7 on Yesterday at 02:51:07 PMA probe slipping and causing a short circuit can quickly damage a lot of components, especially in a high power circuit. Presumably the spark was between the cathodes of CR22 and CR23, which would have bridged the 33V rail to the 12V transformer winding. If it was brief, then I think probably no damage; for a longer period it may damage C26 which is rated for 16V. If you can figure out exactly where the spark/short occurred, that could be helpful. In any case, I would proceed assuming no damage and come back to this if necessary.
It was right near that diode CR22 which I tested
Quote from: sigma7 on Yesterday at 02:51:07 PMThe resistors are very unlikely to fail unless you leave it running for a long time and they overheat.
Check the fuse, but don't turn it on until you have the +33 load installed.
would this be how you do that,
+---[ 910 Ω ]---+
| |
Input o+---[ 910 Ω ]---+o Output
| |
+---[ 910 Ω ]---+
sigma7 edit: fixed up ascii art
Quote from: berskyboy on Yesterday at 03:44:17 PMwould this be how you do that,
+---[ 910 Ω ]---+
| |
+33V o+---[ 910 Ω ]---+o Ground
| |
+---[ 910 Ω ]---+
Yes
Quote from: sigma7 on Yesterday at 04:03:37 PMYes
My board setup, waiting for the resistors,
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https://www.dropbox.com/scl/fi/fu2cyqgla2nxdc5kax2l7/IMG_3777.HEIC?rlkey=zszitm83spzbtxhaidp5id8mr&st=w6oafweg&dl=0
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https://www.dropbox.com/scl/fi/ong6wwhpekxto0cl8e849/IMG_3778.HEIC?rlkey=99qby3k67l5d1j957iogl97r2&st=95307enh&dl=0
Quote from: berskyboy on Yesterday at 05:40:58 PMMy board setup, waiting for the resistors
Looks fine. You may end up needing to move over the big resistor to make room.
While you're making changes, you might want to bring wires out for the -12V (minus 12) and -5V (minus 5) measurements or label those pins. They don't require load resistors, or you could put one 910 ohm resistor on each if you have lots left over.
Quote from: sigma7 on Yesterday at 05:53:56 PMWhile you're making changes, you might want to bring wires out for the -12V (minus 12) and -5V (minus 5) measurements or label those pins. They don't require load resistors, or you could put one 910 ohm resistor on each if you have lots left over.
which one is the -12V and -5V is that under ? like J? -12V, K -5V?
Quote from: berskyboy on Yesterday at 06:04:10 PMwhich one is the -12V and -5V
In one of your videos we saw that you had the schematic. Presumably you used it to make the other connections, so locating these is the same process...
Double check the schematic to see if these are correct:
- Minus 12 at pin W
- Minus 5 at pin 19
Quote from: sigma7 on Yesterday at 06:16:16 PMn one of your videos we saw that you had the schematic. Presumably you used it to make the other connections, so locating these is the same process...
Double check the schematic to see if these are correct:
- Minus 12 at pin W
- Minus 5 at pin 19
NO DICE :(
https://www.youtube.com/shorts/3PCBanL0fks
I will replace the 16V capacitor tomorrow when I get it from Amazon.
Quote from: berskyboy on Yesterday at 08:11:07 PMNO DICE :(
https://www.youtube.com/shorts/3PCBanL0fks
I will replace the 16V capacitor tomorrow when I get it from Amazon.
The 16V capacitor wouldn't/couldn't have the effect of nothing happening.
See if there is 120VAC at the power connector.
If so, check the fuse.
If ok, check the safety interlock switch is pressed.
What was the solution to the problem that changed the "brief turn-on then slow decrease in voltage" condition into the "it works" condition? Was the card-edge not fully plugged in or something? That seems like a good suspect.
If still no joy, measure the +5 Standby voltage on pin 20 (connected to the small switch).
The white with yellow stripe ground wire that goes to the PSU case is missing the lockwasher and nut.
Quote from: sigma7 on Yesterday at 11:07:54 PMThe 16V capacitor wouldn't/couldn't have the effect of nothing happening.
See if there is 120VAC at the power connector.
If so, check the fuse.
If ok, check the safety interlock switch is pressed.
What was the solution to the problem that changed the "brief turn-on then slow decrease in voltage" condition into the "it works" condition? Was the card-edge not fully plugged in or something? That seems like a good suspect.
If still no joy, measure the +5 Standby voltage on pin 20 (connected to the small switch).
The white with yellow stripe ground wire that goes to the PSU case is missing the lockwasher and nut.
Hi Sigma7, good morning, good news... after checking the rear switch and putting alcohol on the connectors. She lives again. Here's the video. (5V, 12V, and 33V) Wow! Thanks so much
https://www.youtube.com/shorts/jBJMnzygqcw
Holy macaroni, what a journey.
Quote from: berskyboy on Today at 11:54:50 AMShe lives again. Here's the video. (5V, 12V, and 33V) Wow! Thanks so much
Congrats and you're welcome. Thanks for your help testing this process!