The +5 V or +12 V on the display connector is missing or low.

+5 V or +12 V missing at the display

Cause: These two come from the driver board, not the display controller. Missing 5 V with the game booting means a connector fault. Missing 12 V is a connector fault, a display pulling the 12 V down, or a failing driver board 12 V section.

Checks

• Measure 12 V at the driver board and at the display. Different readings mean a connector fault.
• Both the same and under 10 V means a driver board 12 V problem.
• Unplug the display: if 12 V comes back, the display is bad (or the 12 V supply is weak).

Fix

• Repair the connector, replace the display, or repair the driver board 12 V section.

Systems

• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• Random vertical or diagonal lines: 12 V missing at the display
• Repairing a missing display line with conductive epoxy
• Dot matrix display power connector pinout and voltages
• Dot matrix display faults
• Outgassed displays and the 5 V supply
• Replace the whole display, not just the glass
• Missing rows or columns on a pin-style display
• Negative HV low and display barely lights

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Three, Clay Harrell (pinrepair.com)