Hi Guys. I got a iMac G5 for relatively cheap about 6 months ago. The guy said he just got the power supply fixed, and the motherboard looks perfect, top and bottom. I took it to apple, and of course they thought it was the motherboard and wanted $500 for a new one.
Then I opened the power supply and discovered 4 blown caps, and a couple had even leaked through the vents in the top. I put it back in the box for a while, until I found my friend who knows electronics.
He fixed it up, and the thing looks brand new. I reassembled it tonight, and hit the power button. No signs of life.
However, after opening the machine, I saw a familiar green LED on the motherboard. LED 1 was lit, like it was before. Then I hit the internal power button, and saw a white glow, and the fan stirred for a split second. I hit it again, same thing, though the white glow was even brighter. Both times, LED 2 lit up. Then after that, no signs from the fan or white LED, but the LED 2 still lit up, and upon holding it, stays lit for a second more before flickering out.
So, what is the problem here? Did I miss a blown cap or something? I checked that power supply from tip to tail, and no other caps were blown or leaked.
I await a response with very baited breath.
... the PRAM battery?
Also try booting with just one RAM stick to see if it's bad RAM.
yes, I forgot to mention I pulled the PRAM battery (wow, a CR2032 in a mac?!), and had it out while testing, then popped it in and tested some more.
I also did a SMU reset, by pulling the power cord for 10 seconds, and holding the internal power button while I plugged in the machine. It only seemed to reset the cycle.
Oh and the external power button does not seem to work. After doing SMU, and putting the case back on, I don't get the white LED to light for that split second.
What i would do is remove everything, unhook drives from power and the motherboard, remove all Ram.
then try to power up to see if it comes on at all.
if it don't there could be other PSU related issues, or the PSU took the mobo out with it. or could be bad caps on the mobo as well.
could be a few other issues as well. i don't know much about the iMac. I am just tossing things at you to try.