Did you try a new ribbon cable yet? I never believed a ribbon cable would make a difference myself, but my F-14 displays were a mess, nothing but garbage on the displays, I thought for sure it was a board problem. But before i dug into that i tried swapping my ribbon cable from my Pin-Bot into my F-14 and everything worked perfectly!

I'd try swapping one of the ones between displays and the display processor board (the individual display cables on each display) then if that doesn't make a difference try replacing the main cable from the display processor board to the MPU.