iMac weird behaviour

[nightwalker]

Hi all! I’m writing for I’m in a deep trouble with my iMac running Tiger 10.4.11. The iMac is a G5 2Ghz PPC with 2Gb RAM and an ATI128Mb video card.
I’m really scared for I’m experiencing a weird behaviour such as: the machine turns off all of a sudden without reason and then if I attempt to turn it on the fans starts and OS doesn’t’ boot at all. Surprisingly, after ten minutes of rest it starts again and I can smoothly work. I monitored CPU temperature: the range is always from 80 to 85 Celsius degree. I performed a pRAM reset without success. This behaviour is casual. Sometimes the iMac runs correctly for days and sometimes I’m not able to work quietly for a couple of hours. I’m desperate for I can comprehend the reason why. Is there anyone who can help me? Thank you.

[HappyLundberg]

You might have a bad power supply or too much dust in the machine, making it shut down to avoid overheating. If I recall correctly there were quite a few iMac G5s with power supply problems and there was a service program on those but I believe it's been terminated.

[wilco440]

I just got mine back yesterday.... same model, same specs, same problem. Random shutdowns.... sometimes it would run for several hours, sometimes only minutes, often it wouldn't even boot. All this happened over three or four days... no problems with dust buildup, excessive heat etc, or at least not that I could see.

Power supply failure, for the second time. The first failure was about two and a half years ago and Apple replaced that PS free of charge, but unfortunately that program ended in December. This time it cost me, but my iMac is back after 8 days (terrific service) and is now running better than ever....

[nightwalker]

Thank you both for your kindness. I’m writing from Italy. The logical board in this country is very expensive (EUR 700.00 circa), so I have to ponder what I’m going to do. As far as power supply I may change it though I’m not sure that’s the real problem. Do you think is there any connection between CPU temperature (though I’m only using Safari CPU temperature is 85 degree Celsius) and power supply? Thanks again!

[Salamander]

Give the air vents at the base of the machine and the big round one behind the stand a good vacuum - no need to take the machine apart. My G5 had the same issue with random shutdowns, 'solved' by an hour or so of rest. After I vacuumed the vents it worked perfectly, fan noise decreased as did the temps.

[cpc6128]

A workmate of mine had very similar problems, took it to apple and it was covered by the recall thingy like this one.. ended up being the power supply.

Apple - Support - iMac G5 Repair Extension Program for Video and Power Issues