Here are the binary patterns.

• 0=0y0000
• 1=0y0001
• 2=0y0010
• 3=0y0011
• 4=0y0100
• 5=0y0101
• 6=0y0110
• 7=0y0111
• 8=0y1000
• 9=0y1001

Stare hard. You will find the answer in the bit patterns.

Once you have found the problem (from the patterns), this is the signal path.

• Generation (origin) at CPU board IC18 (PB0-PB7).00_s6_bcd_signal_origin.jpg
• Transmission through cabling from 1J5 to 4J6.
• Consumption (destination) at master display board IC7/IC8.01_s6_bcd_signal_destination.jpg

Here is the overview of the signal path (forward).

02_s6_bcd_master_display_signal_overview.jpg

To do the actual diagnosis, you work backwards. Start at the problem (incorrect segment display) and follow the signals (arrows in reverse) to find the signal generation (at the CPU board).

Suspect dirty connectors and or halo cracks on cpu display output pins

Re seat display output cables
No?

Re flow pins on the cpu output connectors

1_7bc283cf18a275d9c3cf8e5ede354cba (resized).jpg

I was able to use a voltmeter to see that 1J5 pin 7 on the MPU was not strobing, so 4-7 were never being called up. Found the capacitor in parallel with the PIA pin 12 was shorted. Just left it out since I did not have a replacement. I'll take another when I go over to that location on Wednesday evening.

PXL_20230506_025416822 (resized).jpg

I then was trying to battle the 100's and 1000's digits being flaky to all the player displays. The coin/ball in play are not affected. At the time it seemed that messing with the wiring at the top of the master display board to the player displays seemed to do the trick for that evening.
PXL_20230506_045754174 (resized).jpg

Next day, the displays flaked again. Fun times!
Obviously, I plan to repin the whole game and install new board headers.

IMG_20230506_114204 (resized).jpg