Parts of the dot matrix display don't light, often filling in slowly as the display warms up; dark spots may show in the corners.

Dot matrix display with dark gaps or dim areas: outgassed glass

Cause: The display glass has outgassed: high voltage breaks down the internal electrodes and the gas is no longer pure enough to glow.

Checks

• Confirm the high voltages are correct at the display (see the DMD voltage entry).

Fix

• Replace the display. An outgassed glass cannot be repaired.

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 blank or faulty
• Blank display, garbage or diagonal lines: reseat ribbon cables
• DMD fully lit with no picture while the game plays: bad DMD panel
• Dot matrix display supply voltages
• Which dot matrix displays fit WPC games
• Dot matrix HV parts grouped by supply
• DMD line out from a broken pin at the glass: bridge it with conductive glue

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