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

[sigma7]

urn 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.

[berskyboy]

C25 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.

[berskyboy]

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

[sigma7]

C25 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.

when 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.

my 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.

I 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.

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?
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.

[berskyboy]

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.

It was right near that diode CR22 which I tested

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.

would this be how you do that,

Code Select Expand

       +---[ 910 Ω ]---+
       |               |
Input o+---[ 910 Ω ]---+o Output
       |               |
       +---[ 910 Ω ]---+

sigma7 edit: fixed up ascii art

[sigma7]

would this be how you do that,

Code Select Expand

      +---[ 910 Ω ]---+
      |               |
+33V o+---[ 910 Ω ]---+o Ground
      |               |
      +---[ 910 Ω ]---+


Yes

[berskyboy]

Yes

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