The same segment (B) lights on many characters of the top display where it shouldn't, although display test shows nothing obvious.

One segment lit on many characters of the top display: unsoldered leg on a driver chip

Cause: On the master display board, one leg of the segment driver chip that feeds that segment for the top display (U16 here) had virtually no solder.

Checks

• Work out which segment is stuck on, then use the schematic to find the chip that drives it on the display board.
• Pull the board and inspect that chip's solder joints under magnification.

Fix

• Solder the bad leg and reflow the rest of that chip's pins, the board's connector pins, and any suspect joints where the display glass connects to the board.

The display board carries high voltage; switch off and let it discharge before handling it.

Systems

• Williams System 11A

Games

• F-14 Tomcat

Related tips

• Same segment missing across one 16-digit display
• UDN display driver chips
• Segment missing or stuck only on certain characters
• Characters missing from a display
• Display board chips shown as 4050 are really 4049
• Telling a shorted UDN chip from a shorted display glass
• System 9 versus System 11 display data
• Testing UDN6118/UDN7180 chips for shorts

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