Pinball Repair - Blowing Fuse

Thread Starter


Joined Dec 2, 2011
I have a late 1970's Star Explorer machine that I picked up a few weeks ago. The machine probably sat in a storage garage for 10-15 years. I'm having a problem isolating a bad component on the board. I have a push to hold "fuse" switch (as seen in picture) that overheats and pops 3 seconds after I turn on the machine causing the solenoids to stop working. The only time I can get them to respond is if I hold down the fuse switch causing my bumpers lock in the "on" position and it get very hot.
I believe I've narrowed the issue down to a transistor board (as seen in picture). When I pull this board the fuse does not overheat allowing the flippers work but no other solenoid will fire. I'm assuming that I have a bad transistor but I'm not knowledgeable enough to determine which one is bad or if that IS the issue. Has anyone encountered anything like this before or have any suggestions on how I can troubleshoot this issue?
Another funny thing is one night I could hear a radio station coming through the speaker



Joined Jul 17, 2007
I found another of your threads over here:

Besides the photos, you wrote something very important there:
When I hold it down all of the solenoids work fine except for the bumpers which stay engaged the entire time
So, you need to trace how the bumpers are powered. Apparently, the bumpers (and other things) are powered via the board that you have removed, and it is very likely that one of those transistors failed shorted from collector to emitter. This is causing the bumpers to stay powered, which is a high current drain, causing the circuit breakers' bimetallic spring to open up the breaker contacts, thus removing power from the circuit.

Try to trace the wires from the bumpers to that board, and see how it connects to that board.

Try to read the part numbers from the faces of the transistors Q301 thru 310. The even numbered transistors are probably all the same, and the odd numbered are also probably the same.

It would be very helpful to have a photograph of the underside of that board.


Joined Oct 26, 2011
ok theres not a lot to that board ,set your meter to diode test(or resistance)and check each of those power transistors(check from base to emitter,base collector)and you are checking for this with the small transistors too,thats just for a starter....check D301 for s/c too.....if no faults found trace where the fuse is connected board wise and just generally check for shorts....