My Robocop has just started some strange behavior. It might award an extra ball when it is not supposed to award an extra ball. It might start multi-ball with only two balls locked. Or will lock a ball and light the "ball is locked" light and kick the ball back onto the table. It may give the points earned for the multi-ball or it may not give any points.

All of the items not acting correctly are coming from Switch Drive column 4. Could a bad transistor or capacitor on Switch Drive 4 be causing this action?

Or could it be a diode on the Switch Return side of the circuit? Or is there something else I need to be looking at?

Thanks