One character position stays dark on the displays in every test, while all the others work. Swapping display boards and ribbon cables changes nothing.

Same character position dead on every display: digit strobe wire at MPU J2

Cause: Segment data travels on the ribbon cable, but each character position (digit strobe) comes from the CPU board's J1 and J2 Molex plugs. Here the wire from J2 pin 8, carrying digit 10, was broken on its way to the display.

Checks

• Reseat the CPU board's J1 and J2 plugs and inspect the header and nearby resistor pack for heat damage.
• In display test, check that every J1/J2 pin is pulsing with a logic probe or meter; one stuck high or low points to the decoder chip or the wire.
• Check continuity from the J2 pin through the harness to the display.

Fix

• Repair the broken digit strobe wire (or the burnt connector or resistor pack if that is where the fault is).

The display boards carry high voltage (around 100 V). Do not use a logic probe on the high-voltage display driver outputs.

Systems

• Williams System 11B

Games

• Taxi

Related tips

• Displays dead after the CPU board was removed
• System 9 versus System 11 display data
• MPU won't boot even though a test ROM passes every PIA and RAM: bad game ROMs
• Same segment missing on every digit of one display: loose glass lead
• Using a Taxi/Police Force display board in another 16-digit game
• Taxi and Police Force display board differences
• Displays flash bright and speakers noisy, game does nothing
• Whole groups of coils or all flashers dead: A/C select relay stuck

Source: Pinball Repair help group!! (Facebook group)