Could be the displays. Swap the displays into the 1 and 3 position. If the problem moves its the displays. If not it's in the wiring or the board. Easiest way to test that is to try a board from another machine and see if that fixes it. If it doesn't then it's wiring.

If displays, these are easy to fix. First check the connectors and reflow the solder on the pins. If that doesn't fix it check out Steve Kulpa's page on bally display repair.

If wiring, check the pins on the connectors and replace any bad ones.

Not sure what to do if it's the board.

Steve's page: http://stevekulpa.net/pinball/bally_disp6.htm

faz

Could be bad connector pins at the cpu board for the display output.

I think we're on the right track with connectors, but the digit is only out on 3/5 displays so the enable for that digit is making it from the MPU to the insert panel because 2/5 seem to be working fine. I'm going to guess that the tens digit enable wire daisy chaining between those displays is the issue. Either that or the same digit driver failed on all three displays which seems pretty unlikely.

Sometimes a bad display can cause another display to mimic the failure. Unplug the two questionable displays and try them in one of the known working positions.