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.
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Yes, I've blown 3 3A 250v slow burns, that's a fast acting in there now just for testing it's all I had. Getting more SBs tomorrow.

Yes, F6 Blows with only J2 plugged into the rectifier board.

I didn't suspect the MOV as it was in perfect condition (bad pic wiring in way) RF filter remains possible but could that still be it even when everything runs fine without the F4 fuse in place?

I ruled out anything on the Solenoid board by unplugging all connectors from it and still blowing F6 (wasn't sure if J2 only being plugged into the rectifier board achieved this).

Seems a stuck on solenoid is ruled out as I've never blown the playfield or F4 fuse. (?)

So I'm thinking get some bridge rectifier numbers first (still hoping this is it as its something I wanted to replace regardless)

If that's not it, focus on the RF filter???

Would the only third possibility at this point be a short in the playfield somewhere?

Sorry if my line of thinking is off

TP1 - 2.3 (Low)
TP2 - 232
TP3 - 13.77
TP4 - 6.2
TP5 - Not sure how to get reading without F4 fuse

Pulled all LEDs and all bulbs I've changed out on playfield, still no luck.

Hearing a low brrrr tone coming from around the line filter when it blows. Thinking about bypassing that next to see if that's it before I go about switching out the rectifier board.

Thanks for the post!

Yes, F6 blows when only J2 is plugged in along with F4 fuse, with F4 fuse removed nothing blows.

"If the fuse is not blowing with J2 unplugged the line filter and cabinet wiring is fine." How would I test this as I can't turn on the machine without J2 plugged in?

The coin door lockout is disconnected and the knocker is good.

I removed J2-7 and the machine wouldn't turn on at all. I'm showing J2-7 as "AC Line, low" is this correct? I noticed J2-2 is +43 vdc Solenoid Buss was wondering if you meant that one?