While I'm not totally sure about your board, it looks hacked to me-like the wires from one of the connectors got burnt, and instead of crimping new pins, etc.. they just soldered the wire to the underside of the board. look for missing wires in connector J1, J2 or J3.
I just recently rebuilt 2 Bally AS-2518-18s and 1 of them had similar hacks.
So far for me Steve's page has been $$$. Do what he does

Yeah, that board has been to "hack city". Undo all of that stuff and start fresh with new male/female pins and connector housings. Not sure of your experience with Ballys, but taking the time to replace all the connectors is very much worth it.

If the board appears too compromised from previous hacks, I wouldn't hesitate to buy a repro power supply. It is fun and educational to follow the guide and replace bridge rectifiers and do ground mods, etc., but for the extra $40 (since rectifiers, etc might cost you $20 ) a repro board gives you a new set of everything and you can derive your fun from palying the game instead.

I cringe when i see that. If the person took just a bit more time and installed new headers and crimp on pins things would be a lot better.

Basically your connector probably burned up and instead of fixing the connector they soldered the wires right to the board.

It really should be fixed with all new male header pins and new female pins and housing.