One thing to remember when in search for a spare logic board: They are different in that the number of coins and number of lines played are variations in the boards. Most of the boards have several jumper wires and cut traces on them. I believe Jennings made only one logic board (well, several revisions within the production years anyway), and the technicians added jumpers and cut traces to match the game play. This makes it difficult to have a spare board that works the same as the original board. It would have made so much more sense to use DIP switches on a single production board rather than have a birds nest of wires hanging off of both sides. I'm pretty sure the company got caught up in diminishing returns, which led to its demise early in the game.
Seems Jennings was over their heads trying to market a suitable machine that could adapt to the casino's needs. I feel the machine mechanics had some good design (motorized reels) but severely lacked in electronic engineering. It would have been a good move on their part to spirit a few digital engineers away from Bally when they designed their stuff.