Dual 2.3 GHz G5 suddenly shutting down

Question

We have a Dual 2.3 GHz G5 (production week 10/29/05, Power PPC 970 v.3.0, with 2.5 GHz RAM), running OS 10.4.8. This machine has started to suddenly shut down - like someone pulled the plug with no warning.
After turning itself off like that, we need to wait around 20 minutes before it'll start up again and keep running. Once it has shut itself off, we cannot get to the logon screen without it shutting off suddenly again. After letting it cool down for 20 minutes, it'll run again. So it seems to be heat related in some way.
I've run Temperature Monitor and iStat, and everything looks OK. Of course TechTool Deluxe didn't find anything (does it ever?).
The machine will run for 2-3 hours under load just fine, but will suddenly click and shut off at some point - even when not under a load.
I've checked the System logs and Console logs and can see nothing, except once the system log reported "ApplePMU::PMU forced shutdown, cause = -122"
The other times there was no log entry, like it shut down too fast for the log to be written.
Is the power supply going bad? Is there a temperature sensor which is too sensitive?
We'd appreciate any help or suggestions.

Answer 1

o maybe there is something RAM related, but I can't
imagine that RAM would shut the machine completely
off. Can it?
I believe the problem is thermal related. You may have a processor acting up. Try running Hardware Monitor once, and see what your internal temps are running.
http://www.bresink.com/osx/HardwareMonitor.html
-Bmer
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