So, is it my power supply?

My "machine suddenly goes black sometimes with a pop noise" saga continues.

I have succeeded in lowering the internal temperatures.

But sometimes there is still a random shutdown, sometimes immediately after the power button lights and sometimes after hours or days.

Opened the machine, plugged it in. LED1 lights up. PRessed the startup button on the board inside the machine. LED2 lit up...but after a minute or so, I heard the same soft "pop" and all the fans stopped and LED2 went black.

From iMac G5: Troubleshooting when your computer won't turn on I would then tend the think the logic board should be OK, and this is a power supply issue?

I'm REALLY leery of spending money to fix one issue, then have other issues, and end up spending half what a new refurb would cost-or worse, not even fixing the issue. I've also read that heat can kill RAM, and I was running CPU temps up near 70C before, probably for some months at least.

that sounds a lot like a power supply issue to me. if everything just dies with a pop.

My G5 did exactly the same. Checked the PSU and it seemed to be working ok. Took machine to local Apple Service Center and after running diagnostics they found the trouble was with the logic board. Had that replaced and the machine ran for another 12 months before it died and was sent to the computer graveyard in the sky!