The display isn't right though the voltages look fine.

Display misbehaves with good voltages: crystallised zener joints

Cause: Solder joints on the HV zener diodes crystallise from heat, add resistance and eventually lose regulation, which can kill the display and damage the supply.

Checks

• Inspect the joints on D3, D4, D5 and D6 (D1, D2, D3 and D18 on WPC-95) on the controller.

Fix

• Reflow or replace those zeners.

High voltage section: work with the game unplugged.

Systems

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

Related tips

• Display shows garbage or nothing though the glass is fine
• Dot matrix display supply voltages
• The two negative display voltages must be 12 V apart
• Display voltages low: display or HV section?
• Gas discharge displays need high voltage
• Dot matrix display power connector pinout and voltages
• DMD dead though display and controller work in other games: CPU board fault
• -125 V and -113 V read the same and the display is dark

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