Quoted from cody_chunn:
I would check to see if there's a disk capacitor on the Slam Switch (or any other switch) and replace all of those
^^Agreed, do this first. Replace all of the original switch capacitors on every switch under the playfield that you see. Remember that there are some on switches that are not called out in the manual, so visual inspection is your best bet to start with. The original Bally ones are junk and will die eventually. When they go, they do all sorts of weird stuff. I got a bag from Taydaelectronics.com for my older bally games.