No display at all while the game otherwise works.

Displays blank but the game plays

Cause: The +100 V / -100 V high voltage is missing.

Checks

• Measure the +100 V and -100 V supplies.
• Check the related fuses.

Fix

• Replace a blown fuse. A repeat failure points to the power supply or a short on the display driver board.

The display supply runs at about +100 V and -100 V; switch off before touching the display or its driver board.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• Lower the display voltage to 91 V to extend display life
• Display correct but too bright or flickering
• Score displays weak, dim or dead with fuses good
• High-voltage fuse blows once the display connector is plugged back in
• Displays show only three or four digits at a time in a slow wipe
• Fix the display short before trusting a rebuilt supply
• Measure a rebuilt supply before reconnecting the displays
• Characters missing from a display

Source: Pinball Machines: How They Work & Troubleshooting, Norbert Snicer