I have a 20" Intel Core Duo iMac that only intermittently powers on. Sometimes if I plug in the power it will instantly start and work fine so long as you don't reboot it (it won't start back up). Other times it won't turn on, even if I push the power button, but after 5-10 minutes it will randomly turn on and again seem to work fine unless you reboot it.
I believe it is probably the power supply, but it doesn't look or smell like anything got fried on it. The part number on the PSU is 614-0378 (identical to this one) . When I plug it in and it won't turn on there are no diagnostic lights lit up. I also checked out the power with my multimeter on the 5-pronged connector on the PSU: the two black wires were grounds, the grey ones were giving out ~12V (it fluctuated quite a bit between 11.5 and 12.5), but I couldn't get any reading off of the brown one.
Does anyone know of a way to properly test the PSU? Does it sound like that is the problem or could it be something else? BTW, I already replaced the NVRAM/PRAM battery.