This is the early standard for Bally (title specifically "Supersonic) with an Alltek MPU. I have a pair of display modules that work fine when installed at a certain player position (A), but do not have the leftmost digit in another player position (B). This would seem to indicate that there is no problem with these modules, but rather with the wiring or MPU for position B. (The MPU is an Alltek one.)
I've read the article by Steve Kulpa on these displays, but it address problems with the display modules, not with problems that exist on any display module installed at a particular player position. I've taken a look at the schematic, and it seems that the only different line going to each display is the #6 pin - and I've successfully tested continuity from the boards (i.e., the MPU & display).
I've also done the memory clear procedure (i.e., set the title dipswitches to 01111111, then power up and watch LED #4 flicker off & on every second), but the problem still persists.