Apple MDD PSU - ACBEL API1PC36

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I have an Apple MDD Power Supply made by ACBEL, model number API1PC36 that is failing to turn on.

I have not replaced the capacitors yet, because I was hoping to learn a little more about the unit without just throwing parts at it.

I have read through this thread a few times, and made it to the point where he was checking Pin 2 of Opto M8, where I ran into an issue.

When checking pin 1 and pin 2 prior to jumpering on, I see 5.4vDC or so on both pins, when I jumper on, the fans twitch and both pin 1 and pin 2 go low. At first I thought this was a good sign, until I realized that not only do they go low, but all voltages are lost.

Checking the voltages from the motherboard connector I find the 25v gone, as well as the 5 volts gone.

Before I just go replacing all the caps, does anyone have a good starting point and or procedure for testing a few things? I don't mind replacing the caps, I just don't want to do it only to find they were not the original problem.

Thanks!

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Re: Apple MDD PSU - ACBEL API1PC36

I thought I should add that I have purchased replacement caps to recap all of the secondaries, as well as the startup caps just as a refresh since most of the caps were Teapo.

I just want to ensure that the above symptoms aren't signs of a different failure.

[Toasty]

Re: Apple MDD PSU - ACBEL API1PC36

The thread you read is the longest of them. There are several other threads to help:

https://www.badcaps.net/forum/showthread.php?t=13985

https://www.badcaps.net/forum/showthread.php?t=19206

https://www.badcaps.net/forum/showthread.php?t=14708

The 5v and 25v are standby power, IIRC (been a while since I was in one of these).

The cap that is at the corner of the center heatsink (near the opto's) is the usual culprit, C43.

T

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Re: Apple MDD PSU - ACBEL API1PC36

Thanks Toasty,

At first I didn't want to replace all the caps, I really wanted to determine the fault and replace only that component.

I changed my mind obviously, for two reasons:

1) Improper test equipment (No ESR Meter)
2) If I want this thing to last awhile, $10 in parts for a refresh is not bad at all.

The caps should be here tomorrow. Coincidentally, I have tomorrow off of work.

I'll try to get them all replaced tomorrow and give it a good test run.

Will update here with progress, as well as a list of what I used as replacements for each component.

Thanks

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Re: Apple MDD PSU - ACBEL API1PC36

Replacement caps worked like a champ.

I'm using this as a bench-top power supply.

Installed a panel-mount fuse holder to replace the soldered in fuse.
Built a small voltage regulator circuit using an LM317T fed off of the 28v rail.

All that I have to do currently is drill and mount my potentiometer for the variable voltage circuit, and drill/mount and connect the binding posts for 5v, 12v, variable, and ground.

The only complaint I have so far is that I'm using a 10K pot which makes fine voltage adjustment near impossible. A 2 or 5k pot would be better (even if I dont feel like doing it at this point.)

Thanks again for the help!

[Toasty]

Re: Apple MDD PSU - ACBEL API1PC36

Try these. Super fine adjustment.

http://www.circuitspecialists.com/pr...potentiometers

T