From Pinwiki:

5.12.2.3 All displays are missing the same digit

If all the displays have the same digit out, then the problem is most likely caused by a bad connector at the MPU. The MPU daisy-chains the digit enable signal to all the displays, and if the same digit is out on all, then it's either an amazing thing that they all have a problem w/ the same digit, or the digit enable signal is not present. Check the connectors on the MPU and all of the displays. If all seem well, then one-by-one, disconnect each display and see if the problem goes away. If it does, then there's a short or a bad connector problem on the board you just removed. Be sure to turn the power off between swap-outs, and wait 10 seconds for the high voltage filter capacitor to discharge before you remove any connectors.