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We have a PowerMac G5 that lost power recently. Pulled everything but CPU, still no boot. Does not power on enough to get a diagnostic beep/flash.

When power switch is hit, red light on mobo comes on for a split second, you hear a relay click, and nothing.

After some research, came to the conclusion that it was a bad power supply. Replaced the power supply, and problem persists.

After leaving unplugged for a few days, machine powered on and started to smell like some component was burning, turned off.

Tried to replicate, no power, same light and click as before.

What I am not sure about is whether or not the power supply we bought used is dead as well, or if the problem was never the power supply to begin with. My natural instinct tells me that this is a logic board problem, but not knowing for sure whether or not we receeved a bad power supply leaves me second guessing myself. I know this happens fairly frequently, taking a stab in the dark to see if anyones experienced similar symptoms.

The last thing I really want to do is pull a working machine apart to the last screw just to test this motherboard. These things are a pain to work on.

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It sounds like you received a bad power supply. If you get a smell from the machine and it doesn't power on that normally tells me it is power supply. Unless the capacitors on the logic board are bulging then I would suppose the logic board is fine unless after boot up you see line or the video is breaking up.

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