I recently acquired a SGI IRIS Indigo R4k machine that was nonfunctional. After a bit of troubleshooting I tracked it down to the PM2 (processor module daughtercard, R4400 + oscillator + 1MB cache), which has visible damage to two of the cache RAM chips (smoke holes and cracks). I am trying to trace back the likely sequence of events that lead to this happening so it doesn't happen again. AFAIK in the R4400SC the cache memory is attached directly to the R4400 with the exception of the power leads, and the R4400 has all cache control logic integrated. The PSU voltages have been checked and are within specs, with no excessive ripple. In my experience, chips do not blow up without an external cause that drastically increases the current flowing through the chip, however I also have zero experience with SRAM chips failing in a "spectacular" manner. Is this possible/likely? The other option seems to be the R4400 dying and taking the cache with it. Any ideas on where to proceed from here?