I am new to pinball repair. I'm working on a Williams Space Station (1987) system 11 machine. Machine is great - but I was playing with the sensitivity of the Jet bumper and now the bumper stays activiated (down). Since I'm new to this, I've had a lot of learning to do, and after checking everything I know how - this is what I think I've got:
The switch that actuates the solenoid is not a switch that can be checked with the on-board test. With an ohm meter - there is no short in that switch.
The switch that indicates the solenoid is actuated (bumper down) is tests fine (#60)
So of the two wires that go to the solenoid, the one goes to ground to actuate the solenoid is always grounded even though the bumper switch is not activated.
So now what? Where should I be looking to find the reason it is always grounded?
I inspected the boards visually and don't see anything unusual.

Any help would be greatly appreciated.

Thanks - you got me on the right track. Sure enough a visual inspection of Q77 (A TIP122) looks like it overheated. - I will replace it and its driver transistor - and check the diode. Now I need to figure out what caused it in the first place. Maybe it has the wrong fuse size? Is this common?

TIP122.JPG

I think the somebody who put in the overrated fuse in this case -was me! I didn't check and it was a 2a - I mistakenly put in a five. Anyway I removed the board soldered in two new TIP122's and two driver transistors and put the right fuse back in. Bumpers work again!

I know transistors generally are either good or bad - but I swear the bumpers are stonger than before - maybe just disconnections and reconnections made some better contacts.

Thanks for your help.