Quoted from ForceFlow:
Additionally, check the strips of diodes in the cabinet and on the underside of the playfield. Those are part of the switch matrix, and if one of those is shorted, then you will get odd behavior. Note that you can't replace those with 1N4004 or 1N4148 diodes, unfortunately--you'll have to use a 1N270 or CDSH-270 germanium diodes.
I found plenty of choices on Ebay, I just ordered some for my Joker Poker