imac motherboard repair

+"However, some replacement boards have proven to be faulty, but they are guaranteed for 90 days, and the failures are usually well before that time."+

Thanks, but that is the reasoning I used for only continuing my extended warranty for 3 years, and I still lost.
Also I checked if I could renew Applecare if I had the repair done (insurance that I would be covered beyond the 90 days if it were to fail again) and was told I could not. Perhaps that would seem reasonable to me except that the original problem was identified/known but left to chance. And the lucky ones were in fact those that had the early failures.

Please excuse my previous lack of details:
iMac G5 20"/1.8GHz
My symptoms were:
I found my computer off when I thought I had left it on. At the time I didn't think anything was wrong but it did not respond crisply when I hit the power button to turn the computer on (took 2 or 3 tries). I restarted with the Techtool diagnostic disk that came with Applecare, it ran the diagnostics with no problems reported.
The following day while sitting in front of my computer it popped once and the +screen went dark+ and the computer would not restart. I removed the back but saw no burn marks or smell. I took it to an Apple store and a genius(?) took it in back to inspect it and came out and told me I needed a new motherboard (saw some expanded capacitors) and power supply.
When I returned home I reopened the back of the computer and confirmed what he saw that was not obvious to me at first inspection.
Your problem appears to be different than mine. Sorry I can't help.

Thank you to those who replied (I mean you, Miriam! 😉
I've been in contact through AppleCare and they agreed to resolve the problem by replacing the bad parts, with my responsibility being the cost of labor. This is the best outcome I could have hoped for. My special thanks to Eryn at AppleCare support for the help.

I think they really do it case by case, and I just tried to make the case the best I could for why I felt I deserved some consideration.
I visited an Apple store where their answer was very matter of fact that the computer was past warranty and told me the cost for repair. They were very polite and professional, but it was obviously not their responsibility to go further.

I called Applecare1 (800) aplcare or (1 800 275-2273) and made the best argument I could. I said I had paid for the AppleCare protection plan for 3 years, that I have a variety of Apple products in the home, a .Mac subscription member since near it's inception. My primary argument was that it was somewhat a known issue (article HT2390) and my computer fell in the serial range of the affected computers. And although my computer failed some months after I let the AppleCare lapse, I felt the difference in whether or not your computer failed was really chance, if you used your computer less you were punished because it would fail outside the coverage, where if you were a heavy user your chance to have the problem correctly identified was better.

By the way, the first contact I made through the Applecare support was very polite and professional but again could not offer a resolution; I was transferred to the next level and here is where I think I just got lucky; I found a very sympathetic ear to my plight, and she said that my case would be reviewed further and she would get back to me. Eryn was good to her word and I got a call from her the next day with the good news that cost of parts would be covered and that was enough for me. People do make a difference! I'm really very grateful for that because I think I would have been forced to put the iMac in it's box in the back of the closet.

Good luck, I hope you also get some consideration ..............

My iMac is back from the local Apple store and is working!
.
.
.
.
.
I've also set the /Energy Saver/Options/Processor Performance/ in System Preferences to 'Reduced' (from Automatic).