[weblacky]

I have an unpopular theory as to what's damaging the chips

I'm not saying you're wrong, but DS1780 problems were already plaguing O3K bricks when these systems were new and used by their original owners. Over-voltage glitches are probably more of a power on/power down problem and the typical O3K owner would run their systems 24/7.

Yes....however...not all the "final" SGI systems have this issue.  So I blame individual design decisions (on a bad general design of 5V straight from the PSU to run these things) and the varying quality of each system's PSU model.  Why does Tezro not have this issue?  Why is Fuel the worst?  So on and so forth.  I think some PSUs were better designed and likely those system model that were better matched to their PSU designs did better.  Hence the differing rate of failure of a component they all share in common with the design of their architecture.