I recently picked up an iMac G5 that was described in the ad as "nonfunctional" I guess I got really lucky, because when I got it home I popped the back, reset the PMU (by removing the 2032 and pressing the internal power button, found through Google, please correct me if this isn't how to reset the PMU) and threw some RAM in. Wonderfully, it powered up. Now the strange part starts.
It wouldn't boot off of CD if you put in the disc and held 'c' it would only boot off CD once it got to the question mark Mac screen and you put the disc in, otherwise the Superdrive would kick out the disc. If you put the disc in after the question mark Mac screen, it would boot right up, happy as could be.
I threw an 80GB Western Digital SATA hard drive and 1GB of Kingston RAM in it (in addition to the 512MB of Samsung RAM that was already in there and booting perfectly) and then it started getting temperamental. It would start, Apple chime and all, with the back casing on, but it wouldn't get past that point, no matter how long you waited. No VGA would ever appear, and it, to the best of my observations, would not boot off the optical drive. Take the case off, and it would chime and VGA would pop up. At this point I started taking note of the length limitation on the RAM, and perhaps the fact that it could be shorting on the CPU heatsync. Measuring the RAM proved that it was slightly less than the maximum 31.75mm tall.
8 hours later: The iMac won't start up at all. Case on or off, the LEDs are as follows:
Pressing the power button causes them to go to this, but only for a fraction of a second:
And then they return to:
I've checked all the capacitors, both on the logic board and in the power supply, none of them are bulging and they all look as good as they would've brand new. I've modified and ATX power supply to give the iMac what it needs (aside from the 24V for the LCD inverter) and it powered up perfectly on that, however it did not go into disk target mode when holding down the 't' key. I replaced the ATX supply with the original, and it started up once, but this time without the third LED lit (LCD communication)
As it stands right now, neither the Apple PSU (which I've hotwired and tested all the voltages on, it's good) nor the modded ATX PSU (which I also measured voltages on) will power up the machine. If you press the power button, it will power the two left LEDs for a fraction of a second, and a faint clicking noise can be heard, and then the computer goes dead again.
I'm just unsure of how all this happened. No static discharges occurred, and the unit was unplugged when I was doing any work inside, aside from having the back case off to test the RAM issue. I know the symptoms sound like they may be blown/bulging caps, but all the caps are PERFECT. The power issue sounds like either a PSU or a cap issue, but given that I've tried with two PSUs and the same issue arises, I'm just unsure. Are there any capacitors on the opposite side of the board? I haven't removed the board yet to look. I've replaced blown caps on PCs before, so I'm sure none of these are bulging/blown, and I've done modifications to iMac G3s and PowerMac G4s before, and the ONLY other time I've experienced something similar to this was when I had a G4 "Mystic" and my +28V source was dead.
Attached picture is without the stock PSU inside the iMac, if you were wondering what was missing from it.