Have you isolated the problem to the board, as in disconnected the playfeild switches and jumped the pins to see if it is doing the same thing ? I had a recent problem where the diode was shorted to ground on one of my switches cause a similar problem. Otherwise on the board I would check the *going from memory* SIP resistor packs, the component that looks like a straight line with 9? legs somewhat in the middle of the board (as I recall they don't make the correct one anymore and you have to modify the replacement by cutting off one leg