How to fix an old HP41cx

[GreyUser]

That’s in decent shape, hardly a mess. The zebra connectors for the processor board are fine with nothing missing. The case bottom is a bit rough and it is missing the two upper battery connector locator/centering pins. That can be repaired with some styrene bar glued into place but it’s not the issue with intermittent behavior.

The bigger issue is your described problem. Since the bottom posts are sound, it sounds like a defective rom or ram chip on the processor board. The only way to troubleshoot is to substitute the processor board, this will tell you if the original board is the problem. To repair a bad rom/ram, you would need a service module and a donor processor board for the replacement ic’s.