I’m working on a Bally 2518-22 SDB for a friend. He brought over a box of crap and would like me to see what I can do. I have very little experience and knowledge, but would dive in and try. I’ve been able to get 4 up and running 100% and that feels great. BUT, he has one that locks on ALL playfield coils at power up and blows playfield fuse. It came in that way. I’ve rebuilt J3 andJ4 with new pins. Checked tip102 transistors and they measure normal. Thought it might be the U2 chip on the board, it was nasty looking. Pulled one off another parts board and no change. So what would lock on all coils at power up? All driver board test points are within range.
Thanks for any help.

Hey Quench, thanks for offering the help.
The board is on my homemade test bench. I unplugged J1,J2, and J5. Turned on power and system booted up in attract mode.
With game in attract,
U4 pin 3. 5.08v
U4 pin 2. 2.06v
CR15 non 2.06v
CR15 banded. 1.31v
Q15 tab. .59v

With game started,
U4 pin 3. .49v
U4 pin 2. 2.05v
CR15 non. 2.06v
CR15 banded. 1.31v
Q15 tab. .59v

Hope this makes sense. Here’s a couple pics. I’m headed out of town for a couple days, but will be back to respond with anything you recommend. Thanks much, Damon

1796A2F9-C067-4224-B857-C3AC6F3C7AFA (resized).jpeg

7A41243C-949E-475C-B835-3239AF430E36 (resized).jpeg

Thank you for your help. I will work on changing U4 tonight and report back. I have done new caps on all the boards with originals existing.
Honored to have the best offering advice. Quench, Big Al, and Ed!! Trifecta.

Ok. No finish line yet for me. chip U4 change went well. Desoldered U4 off parts board and set onto SIP pins. Straightforward. Plugged in all connectors with fresh playfield fuse and powered up. I can’t confirm that ALL coils lock on, but it sounds like many do and blows playfield fuse again. Brought out the multimeter.
Game in attract mode flipper relay off.
U4 pin.3. .89
U4 pin 2. .35
CR15 non. .35
CR15 banded. .01
Q15 tab. 45.1

Game mode relay on
U4 pin3. .51
U4 pin 2. 2.03
CR15 non. 2.03
CR15 banded. 1.3
Q15 tab. .6

Thanks

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We have a winner!! Using your chart, I checked U1 pins and they were good. Then U3...too high. Swapped out and all is good now. I also changed out C23 cap and tested on my Paragon. It’s a 100%.

So, I want to try to wrap my head around this the best I can. I wish I had been taught how to read a schematic rather than years of wasted Spanish. If I have a coil not functioning, and I briefly ground the correct tab and it fires the coil, that confirms connection to that coil is good. Then test the transistor, diode and resistor. If they test in line, then check U1-3-4 pins to see if a transistor is bad on one of the chips. What does U2 do? If U1,3 and 4 have 7 transistors each, that’s enough to cover the whole game.

Yes Ed, thanks. That explication was gold! Till that last paragraph. Haha. I really think that this is becoming much clearer and I will be placing a order with you soon.
You guys are awesome. Thank you so much.