- Confirm continuity for connectors to and from switches (optos) in question.
- Actuate drop target in switch test to see if they change states.
- Determine if switches are part of matrix. If so try manually activating switches with rows/columns on driver board. Doing so can help rule out a board problem. And narrow the issue down to the pf.
- Test voltages at optos. There may be a change of voltage when changing states.
Note: I do not have nor have ever worked on this game. Just some thoughts as I read your question.