Proslant

[Crash0]

Hello all,
I recently acquired a Bally 5500 Pro-Slant Red Hot 7's. Having an issue or 2 getting it up and running.
I have replaced the power supply,and battery after that I got a little life to the machine. Displays ect...
I got the safe ram chips attempted to perform as instructed. Nothing on display to indicate it has done anything.
I have a prom reader and checked the safe ram chips, U12 was bad, U15 was ok. Have a new set on the way.
Tonight I pulled chips out of the MPU 1 by 1 and tested them. All were good except the U12.
Now, my question is, could that be a coincidence or is there something that might possibly just causing that particular socket to go bad?
If so, should I replace MPU, and if the case should I go to a 6000 board, and will I need anything else to do that?
also need to know where I might be able to find a U12 ME900000-A-1. Haven't had much luck locating any as of yet.
Thanks