Running until warm? Socketed eproms (usually 28 legs and labels and little windows) start to become crook at elevated temperatures.
Eproms with this problem can be read after hitting with a can of 'cold' and then burn a new one (if you can find one of that type).
If you don't understand this bit, leave the repair to experts, but by all means try the cold treatment, provided, opening a cabinet door doesn't defeat you.
Run a COLD air stream past the boards, if you can, and see if it survives past lunchtime.
See WARNING below before unplugging anything.
Re-seat all the PCBs, but this might ADD a problem, WARNING: If you pull one and the backup battery disconnects, that board or others might become a zombie.
Old dirty microswitch? Oil in a switch? Bum connection in ESTOP chain? Give all wires a tug and hope none come off in your hand.
Continuously flexing looms/cables/connectors? They are 28 years old now. Are some strands on there last legs?
Round blob style diodes if there are any? Look first at orientation, give them a flick. Bingo!! gone! The wire bonding at the blob has aged beyond usefulness.
Experience here pre-dates when IC's came into use!!!
The 'old eprom' is a most likely culprit, if wiring/switch problems are not there, and it passes the flick test.
Super X3. 3600rpm. Sheridan 6"x24" Lathe + more. Three ways to fix things: The right way, the other way, and maybe your way, which is possibly a faster wrong way.