Quoted from Grasshopperski:Just got finished checking things out and here is what I found:
Solenoid test, low and behold jet bumper is now working, (I checked all of the fuses all good)
on score display 3 and 4 it said error 28
In solenoid test, the CPU fired the jet bumper. So the solenoid firing circuit is good, the MPU is just not being told to fire the jet by the ball during gameplay. You have a problem with the special solenoid switch/wiring that is triggered when a ball hits the jet bumper. You won't get a switch matrix report from this switch, there is a secondary switch for scoring that is activated by the jet bumper mechanism AFTER it has fired. The scoring switch is the one that reports to the CPU, and it can only do so after the coils fires, so it is of little use to you for troubleshooting. This is why it said error 28, because the secondary scoring switch had not been activated in 60 balls or 20 games.