This Robotron was working strangely. The Move stick was “stuck” on move left. It was also throwing RAM Error during the self test.

David bought some compatible RAM chips and we fixed that issue.

The Control problem was tougher. We swapped the control translation board from Defender, but that did not work. The controls were all messed up then.

Back to the proper board which has 3 ICs in the middle that accept the input from the controls and send it to the right pin on the main PCB. These ICs are pretty much a series of signal inverters. Closed switch send +5 to the pin, open switch sends 0. We test each set of pins and found one that migrated between 3 and 1, not enough for a real signal but more than 0 so the PCB thought it was in Move Left the whole time.

Swapped a chip from that Defender and plugged it back in. Working like a champ.