What condition (electrical, software, mechanical) can cause a "check field fuse or FU1 fuse" error message during game play when there is not a problem with either fuse? Pin is a Bally Dungeons & Dragons 6803 MPU and the error occurs randomly, sort of, but always when a ball is being held in the left or right teleport. I have checked all fuses, replaced the power board with a brand new board and replaced both opto boards in the ball trough. Switch test during diagnostic mode inbdicates all switches are open. Since the error only occurs when a ball, or balls, are held in either teleport, it seems like whatever is contolling them would have something to do with it but I am at a loss as to what to look for now. Transistor, memory chip, capacitor on the solenoid, loose connection? I have not reflowed the pins on the memory board. Any suggestions would be appreciated!

I thought so too, but I replaced both opto boards with brand new ones. Also replaced the power board. Could a flakey chip or bad connector on the MPU cause that kind of problem? It only happens when a ball is being held in either of the two teleports.