Just finished reassembling a project Silverball Mania and amazingly it booted right up on the first try. Apart from some switch issues, the game started, flippers work, and scored as expected, but the only coil that would fire was the right pop. Didn't work in game or in test. After testing a few things, I grounded each coil's transistor and they all fired fine. I put the ball back and hit start for the hell of it, and all of a sudden every coil worked! I probably played 30 games trying to adjust everything, then just like that they all went dead again.

Flippers still work fine, but the only coils I hear in test are the coin lockout and a relay in the backbox.

I have 45v at every coil, and every coil will fire when directly grounded to braid. Every coil will fire when its transistor is grounded. Every transistor tests at .42 or .47

F4 tests good out of its clip. The two fuses under the playfield were 3A so I replaced them with 1A and watched when i powered up. Didn't blow either.

I've re-seated all the connectors several times while pulling the boards to look for obvious broken traces or cold joints, and it all looks pretty clean. The fact they all came and went at the same time has me thinking logic issue somewhere, but not sure where to look at this point?

Slochar, that jumper is present and I have continuity across those pins. I also see the expected 5v at TP3.

Barakandl, that answer was WAY past my skill set! Put it this way, I did just dig out the logic probe I bought but never opened!

So it looks like the black clip to ground, the red on 5v? Which I can get from TP3 on the driver board correct? Set probe to TTL or CMOS? From there, which pin(s) am I probing on those J4s, and I'm guessing put the game into solenoid test mode while I'm doing this?

Appreciate the help guys!

I still have 45v at all the coils, and they all work when their transistors are grounded so I think power is good.

Thanks for the details on the logic probe barakandl - all of those tests came back as expected. Driver J4-7 and U2-19 were low during solenoid test, high during sound test, and U2 20-23 all went HIGH to LOW during solenoid test.

I replaced the pins and headers on MPU-J4 and Driver-J4, and confirmed I didn't bridge any two pins that shouldn't be. Also had good continuity on the connectors between those two plugs. It still won't fire.

I noticed the driver board is not Bally but a Stern SDU-100 (10-24-78 Rev C). Assuming that's fine since those solenoids did work for a bit. I do have an Eight Ball Deluxe with the Bally AS-2518-22 driver board that works great - could I swap that into SBM to test? Figure if that works then the problem is somewhere on the driver board...

I installed the EBD driver board and all the coils work, so definitely something on the board itself. I'll replace the rest of the headers while the original board is out and keep testing once it's reinstalled. I appreciate being able to add the logic probe to my bag of trouble shooting tools, so thanks again for the hand holding!

The silver lining in all this social-distancing is that I finally found the time to get back to this one! I used the good SDB to get this pin dialed in and working 100%, so that's a pretty good baseline for going forward.

I replaced all the headers on the original board, and when reinstalled it's right back to the same symptoms - no coils. The outputs on U2 look fine as pins 7-11,13-15 all sit high and pulse low during solenoid test.

So I've replaced all the headers and pins with Trifurcons on the MPU, Stern SDB, and Rectifier boards, also I've done the ground mods and tied TP1 and TP3 together. That got everything working except the left sling and, intermittently, the right pop bumper.

Both of those still fire when the transistor is grounded so it must be upstream from that, right? Now if I'm reading these schematics right (huge IF), the signal to fire the left sling looks like this:

U2-11 - goes low during solenoid test
R67 - tests good
U3-2 - goes high during solenoid test, and all of the transistors on U3 test good.
CR9 - tests good
Q9 - tests good (brand new TIP102 for shits and giggles)
J5-9 - re-pinned a second time - see above.

The switches register in test, and the sounds and scores are there in gameplay, just no coil action on either.

Just to double check, I reinstalled the Bally SDB and everything works perfectly. What am I missing on the Stern board? I assume the schematics are valid for both boards?

Oh just remembered to check C23, which is coming in at .300vac. Pretty sure that ain't good! Could that be the root cause of these two not working correctly or at all?

I did. The wire checked out and later on I replaced J3's header, pins and connector. Just curious though, the TP1 to TP3 jumper mod just reduces the strain on those pins; it doesn't eliminate the need for the wire between 13 and 25, right?

IT'S ALIVE!!! This is the nugget of knowledge I've been searching for - I wasn't aware of that trick to test the diode. It was reading .48 just like the other diodes in that area so I assumed it was good. Replaced CR8 and CR9 and both the sling and pop are working great now! I guess the moral of the story is you can't always trust the multimeter test with diodes?

I learned a ton troubleshooting this one, so thanks again to everyone who contributed!