Update
Updating database... Please wait.
Wednesday 7 March 2018 at 19:31
1) If you slowly turn up the display voltage on the Solenoid Driver board (towards 190V), does that digit then start working?
2) The schematic picture you posted above shows four pins connected to the A5 digit. Unsolder them one at a time leaving the unsoldered pin floating in the centre of the hole...
Source: http://pinside.com/pinball/forum/topic/stern-6-digit-display-problem#post-4267941