I won a local auction for an Apple Lisa!!!

[sigma7]

The 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.

[berskyboy]

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.

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

[sigma7]

I 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.

The 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.

[sigma7]

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.

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.

[berskyboy]

I 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.

The 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

[sigma7]

I'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.

Fuse 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.)

E6 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?

[berskyboy]

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

[sigma7]

Any 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.)

[berskyboy]

Any 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

[sigma7]

yes that was after I reflowed it.

Where was the short? ie. between which two pads or traces on the circuit board?

[berskyboy]

yes 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

[sigma7]

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?

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.

It 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?