Mac Classic Analog Board - Clicking sound with oscillating 12v and less than 1v on the 5v rail

[oliviaiacovou]

Recapped this analog board because it took minutes to charge up the caps and to get to a working voltage, however since recapping I only get the issue described in the title. The same issue occurs with and without the logic board, and I’ve also recapped that too. Any ideas?

 

[bibilit]

Caps are not enough to get those going.
There are several parts to replace as well (diodes, Optoisolator…)

 

[oliviaiacovou]

how would i go about testing these or do i just go ahead and replace them all?

 

[bibilit]

The opto cannot be tested and testing diodes is not accurate as those are not shorted, just leaky.
So replace parts as a matter of course.

 

[Phipli]

The opto cannot be tested and testing diodes is not accurate as those are not shorted, just leaky.
So replace parts as a matter of course.

Wait... Optocouplers can be tested with a diode tester? Is there something strange about that one?

Also, diodes don't leak and are possible to test.

Edit : ah, you mean leak current, sorry, I thought you mean some kind of fluid.

If they're leaking current you can test for that too.

 

[oliviaiacovou]

Wait... Optocouplers can be tested with a diode tester? Is there something strange about that one?

Also, diodes don't leak and are possible to test

i already tested the opto and it seems fine, should the diodes have continuity going one way and not the other? just need to check because i can't find any working ones

 

[Phipli]

i already tested the opto and it seems fine, should the diodes have continuity going one way and not the other? just need to check because i can't find any working ones

Does your multimeter have a diode test function? Lift one leg to test it.

 

[Phipli]

i already tested the opto and it seems fine, should the diodes have continuity going one way and not the other? just need to check because i can't find any working ones

How did you test the optocoupler?

 

[dochilli]

There are a lot of parts on classic AB that can be defect. Most often: DP3 and DP4 (1N4148), TDA4605, CNY17G, IRFBC40. I would replace them all.

 

[oliviaiacovou]

There are a lot of parts on classic AB that can be defect. Most often: DP3 and DP4 (1N4148), TDA4605, CNY17G, IRFBC40. I would replace them all.

Will do. Ordering those now, will update when I've got them all in

 

[oliviaiacovou]

I would replace them all.

Just replaced them, no change

 

[Cam]

I'm having a similar problem (12v won't go above 10v), and I'm starting to wonder if the caps need a low ESR value?

 

[svenvendetta]

Welcome to the world of pain the Classic AB has brought to many lives as I documented here. Rooting for you to find a fix and watching as the problem is pretty much identical to the one I'm having.

 

[Kouzui]

I'm having a similar problem (12v won't go above 10v), and I'm starting to wonder if the caps need a low ESR value?

Just replaced them, no change

How many caps did you replace? I recently did a couple classic analog boards, and I only replaced the caps indicated on recap-a-mac (as well as the two large ones near the flyback), and didn't have any issues. No diodes replaced, either. I suspect that the orange caps might be low ESR, so if you went scorched earth and replaced them, then that might be an issue. None of the ones recap-a-mac recommends you replace are, though.

 

[oliviaiacovou]

How many caps did you replace? I recently did a couple classic analog boards, and I only replaced the caps indicated on recap-a-mac (as well as the two large ones near the flyback), and didn't have any issues. No diodes replaced, either. I suspect that the orange caps might be low ESR, so if you went scorched earth and replaced them, then that might be an issue. None of the ones recap-a-mac recommends you replace are, though.

I replaced only the ones on recap-a-mac, and I currently have the originals back in because I thought the ESR might be an issue, because I know the caps worked before, just slowly

 

[bigmessowires]

I'm wondering if the sound you're hearing is the "flup" of the power supply repeatedly attempting to start and then resetting when it hits a failure condition. I think this term originally came from the book Macintosh Repair and Upgrade Secrets. If you search the web for "flup" or "flupping" you'll find plenty of relevant discussion.

 

[oliviaiacovou]

I'm wondering if the sound you're hearing is the "flup" of the power supply repeatedly attempting to start and then resetting when it hits a failure condition. I think this term originally came from the book Macintosh Repair and Upgrade Secrets. If you search the web for "flup" or "flupping" you'll find plenty of relevant discussion.

the clicking comes from the speaker, would that still be the same thing?

 

[bigmessowires]

See discussion of flupping that begins on page 117. https://vintageapple.org/macbooks/pdf/Macintosh_Repair_&_Upgrade_Secrets_1990.pdf

 

[Cam]

How many caps did you replace? I recently did a couple classic analog boards, and I only replaced the caps indicated on recap-a-mac (as well as the two large ones near the flyback), and didn't have any issues. No diodes replaced, either. I suspect that the orange caps might be low ESR, so if you went scorched earth and replaced them, then that might be an issue. None of the ones recap-a-mac recommends you replace are, though.

I replaced all of them, since I saw that shiny 'hey, I leaked' deposit all over the place. So I pulled them all, cleaned the board and replaced with new caps. I'm going to order new low ESR caps based on the list from Amega of Rochester (https://amigaofrochester.com/recap-services/capacitor-list/) which I didn't see before I did the cap work

 

[Cam]

Well, the new low ESR caps did the trick!
After weeks of playing with this horrible AB, it chimed and came right up.
Might help someone else?