On one score display the bottom segment (segment d) of the digits is missing, and the fault moves with the display when displays are swapped.

Gottlieb System 80: bottom segment missing on one display that follows it: replace Z1

Cause: If the problem follows the display, the fault is on that display's own board; here the Z1 driver chip that drives segment d (pin 15) had failed.

Checks

• Swap the display with another to confirm the fault follows it.
• Reflow any cracked joints on the display board connector first.
• Check Z1 pin 15 and the segment d trace.

Fix

• Replace Z1 on the affected display.

The displays run on high voltage; unplug the game and let it discharge before handling them.

Systems

• Gottlieb System 80
• Gottlieb System 80A

Related tips

• Missing segment on one or more score displays
• Missing digit on one or more score displays
• Display chips on the CPU board fail after swapping displays
• Display fault: board or display?
• Restoring brightness on 4, 6 and 7 digit display boards
• Guarding the fill tip on the back of a score display
• Gottlieb Futaba displays run on low voltage
• One six-digit display completely dead

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