I recently received a 1979 Bally Star Trek pinball machine from my father. Most everything was working well when I received it. I did need to replace the sound board and I threw some led lights in the back glass and replaced all fuses (with proper ones). Probably ran about 100 games or so through it over the course of 2 weeks. Mid-game one day she died on me.
I checked and the F6 fuse was blown, I narrowed it down to it only blowing when the F4 fuse is in place, and it also blows when only the J2 connector is plugged in. I checked all coils and am getting 10+ Ohms on all. I’ve gone up and down the play field 4-5 times and see no signs of anything fishy. F4 is the solenoid power supply and could fail as a result of bad BR3 rectifier or shorted R3 varistor (looks fine). But F4 isnt failing, F6 is only blowing when F4 fuse is in place. The R3 Varistor looks perfect, there is a place on the wood behind it that suggest one has most definitely blown before but the current one looks good. So I’m curious if the only real possibility is a bad bridge rectifier.
Also noticed I’m only getting about 1 volt (5.4 to 7 needed) on TP1 for switched lights on play field and backbox but can’t really see if they are working correctly as game won’t full boot with f4 not working.
Could a stuck on solenoid be causing this? I’m kind of hoping it is just a bridge rectifier to be honest because I wouldn’t mind just purchasing a brand new rectifier board all together since this one is original and 40 years old.