I'm restoring a MrMrs Pacman and have it all restored except for a troublesome problem with displays. When I got the pin three of the displays were messed up. I found an old Bally display that worked fine and got two new pinscores. With everything connected one of the displays is bad. I've tried two Alltek MPUs and two different Solenoid Driver boards. Moving the displays to all different combinations, the problem moves with the displays.
Here's some pictures.
With player 2 disconnected and player 1,3,4 connected: All the connected displays look good in attract mode.
With player 4 disconnected and player 1,2,3 connected: All the connected displays look good in attract mode.
With all displays connected: Player 4 is off on 00 (current game) score and all 1's when showing high score in attract mode.
With all displays connected: the diagnostics run fine: 0-9. All displays work fine.
With all displays connected: Playing a 4 player game player 4 doesn't show. But if I unplug player 2 then player 4 shows fine.

Is there a problem mixing pinscores and Bally displays? I've not had issues before.
I've verified connectors. I plugged up the intermittent Bally display that barely works (missing segments and blinking) when used in player 2 position, all 4 displays work in this scenario, although player 2 is barely hanging in there.

What should I look at next?

Player 2 disconnected
IMG_8305 (resized).JPG

Player 2 disconnected
IMG_8306 (resized).JPG

Player 4 disconnected
IMG_8312 (resized).JPG

Player 4 disconnected
IMG_8314 (resized).JPG

All players connected
IMG_8308 (resized).JPG

All player displays connected
IMG_8315 (resized).JPG

All connected in display diagnostics (good test)
IMG_8316 (resized).JPG

Whoop whoop!
I had a hypothesis that the player 2 and player 4 displays' latch strobe must be having a problem since one of the displays wasn't lighting up at all during game play. The latch strobe wire is J1-15 pin on the display.
So, I disconnected all displays and verified continuity from pin 15 of each display all the way back to the corresponding pin on J4 of the mpu connector.
Here's that path that the wires for pin 15 take.
Player 4 - goes to player 2 pin 11 (not used), to player 1 pin 17 (not used), to the block connecter and on to A4J1-23.
Player 2 - goes to player 1 pin 11 (not used), to block connector and on to A4J1-21.
Player 3 - goes to block connector and on to A4J1-22.
Player 1 goes to block connector and on to A4J1-20.
So, I had verified that if the mpu is sending latch signals to the displays, it should be arriving at the display.

Now, these wires on player 2 and 4 I can only assume were being connected to unused pins on other displays in order to just dress up the wire harness so that wires aren't floating around.

I connected the displays back up and tested continuity of adjacent pins on player 4 and player 2. I found that with the connectors attached to the displays, player 2 display pins 11 and 12 were shorted. So, I just removed the wire that was punched down through pin 11 and let it float above the connector. With that short gone, all the displays work perfectly now!
Hope this is helpful to you all.
Cheers.