My Ubuntu PPC server is having hardware problems.  It will just intermittently shut off.  I've reset the SMU and the PRAM, vacuumed out the guts, reseated the RAM, pulled any possibly problematic 3rd party boards, and it still crashes.  I was watching the syslog and it didn't look like a thermal shutdown, though it acted like that.  The only thing I can think of is a power supply problem, so I'm going to see if I can find an inexpensive replacement.  In the meantime, this machine will be offline for a couple of weeks at least.