[This was extracted from a large article about getting a dead Joust operational. I thought it made sense to put this part in its own post to help anyone else with a similar issue. It may reference content from the previous two posts here and here.]
…So now I have a Joust that boots correctly and comes up into its attract mode normally. However, after coining it up and starting a game, I still have some issues – player 1 starts running to the left non-stop!
Opening the control panel shows the switch is not stuck, and disconnecting its harness did not change the behavior, so I have another board-level issue to resolve. The input board multiplexes two sets of switches into a 6821 PIA, and the switches come in through one of two header connectors on the board.