Hey Wiz
It seems like whenever I have seen this error before it is usually traced back to one of the socketed chips not making a good contact. Either one of the sound board Eproms or the ASIC on the MPU board. Removing and reseating usually helps. Some good info from Ed at GPE about the ASIC here. https://www.greatplainselectronics.com/Information.asp?region=139
Wally