In an effort to rule out the power supply causing the XL1201's instability, I sent it out for overhaul by Power Clinic. After reinstalling it, I booted the XL1201 and just let it sit in the
Unfortunately, the computer decided to reboot itself after about 15-16 minutes. So, the power supply would seem not to be the problem.
I will have to disassemble the XL1201 and give it a thorough examination to see if there are any obvious physical defects. If none are found, I will try to remove, clean, and reseat all socketed chips, and see if that helps.
I still have a feeling that the capacitors on the backplane and/or the two boards could be the problem, but at this point I just don't know. It worked fine for several weeks (including one or two days of overnight runs) before becoming unstable.
Power supply before picture:
Power supply after overhaul picture: