Tested my Macs PSU with a voltimeter and got:

3.3v
5.09v
11.90v
28v

All of the lines seem okay (12v line a little low). The machine randomly shuts off, especially under high loads. Could it be a case of undervoltage/overvoltage?

Hope I don't have to shell out $235 for a new one.

umm did you say MAC....

but test it under load and idle and see what the drop is, if it drops alot then that's most likely the problem.

Yes, it's a Power Mac G4 tower

Reseated the Power supply connecter, same voltage readings, but no shutdown so far.

I could pop a standard PC ATX power supply in there, but i'd have to figure out how to mod it to supply the nonstandard 28v to the mobo.

uuum, leave it its stock, right

So, apparantly these power supplies are plagued by the bad Chinese capacitors that were used a few years ago.

Would a PC power supply blow if I used a DC/DC converter on the 12v line to make 28v?

The G4 mobo and case will take an ATX supply, however it will need to be rewired and the 28v supplied on an extra two pins(which is the main problem). Plus, I dont want to pay nearly $250 for another measly 380w PS that probably also has bad caps.

uh did u say Mac??????????????????


Did you say mac?


ouch, Im sorry dude, are prays are with you...

I recently opened up 2 dead ATX (250W) PSU's, the symptoms had been similar to your own... random shutdowns/reboots etc. the 2200mF 10V's were totally 'bulging' and considering the cost of these caps' < $1.50 each, were I looking @ a $250.00 bill... I'd suggest replacing them (if you felt confident) the process is easy enough, recently repaired 2 m/boards (similar problem) details @ site in sig'

call apple. they can help you alot more than us mostlikly

I think I fixed it! :crosses fingers::

The CPU card needs to be secured to the mobo with 3 screws. My dumbass only put two in and forgot about the third.

PSU must have been sensing a funky ground on the CPU card and would shut down the computer, b/c the Darwin log file would say "ApplePMU:: Forced shutdown cause -122"

Hopefully the bad ground was the only problem.