Doughbroz
New member
Original 1981 model. Intermittent problem, sometimes works ok for hours, sometimes can not get it to stop scoring by itself. Shows as stuck switch 12, which is a daisy chain of one rollover button and three standing targets. It's not a stuck switch, because if I hold any one of the four switches closed it stops scoring, so I know the switches are ok. When I release whichever switch I am holding closed it may take anywhere from five to thirty seconds before it starts scoring again. It may score anywhere from three to twelve times, then will stop for a few seconds and show zero in the four digit display, indicating the short, wherever it is, has opened. A few seconds later it starts scoring again. I can't see a short of any kind and it's not a bad connection on the MPU board. When it's working ok, pounding on the playfield has no effect, so it's not a bare wire or tab bent out of shape and shorting out. I suspect a bad diode on one of the switches, but they are so damn hard to get at, so I am hoping someone might have an idea if there is a way to narrow down the problem to whether it's in the playfield or on the board. I do have complete schematics, the circuit in question enters the MPU board at pin 11 on connector A4J2. Any help appreciated. Thanks