An update on this — done absolutely loads of troubleshooting:
- Installed brand new 16MB eight chip SIMMs in bank A, with the stock 1MB SIMMs in bank B
- Installed the stock RAM in Bank A, with some more eight chip 1MB SIMMs in Bank B
- Tried the just the 16MB SIMMs in Bank A
- Went back to the 8MB config
- Removed the 4GB SCSI hard drive I installed, and put back the original HD40 with a clean install of System 7.1.1
- Reflowed the connections to the PAL chips
- Reflowed the connections to the ROM socket
- Checked all the traces from the ROM socket to the CPU for continuity
- Checked PSU voltages with a multimeter
None of the above made any difference and my symptoms are identical to
@beachycove. Random bus and address errors - or just lockups - particularly on cold boot. Also, invalid checksum err on known good disk images is another symptom that pops up when the SE/30 isn’t happy.
It does feel like a RAM problem, but I’ve tried all these different modules, so it probably isn’t.
One thing I did look at carefully is the way the ROM SIMM fits into its socket, because I’ve had issues with an intermittent connection. It seems that, using a rubber band to give it support, keeping it held as far forward (past the point where it clicks into the slot) as possible has helped with stability. In fact, it helped so much that I actually thought I’d solved the problem the last few days as it’s been running so well. However, it just bombed out on me while I was changing a desktop pattern this morning so there is still a problem.
It’s downheartening that it’s not working reliably but one way or another I’m determined to get a fully working SE/30.
Next step is to put the motherboard in the dishwasher and then dry it out properly. I also plan to recap the Sony power supply as there is quite a lot of electrolyte goo on the board and it would be good to rule this out.