The display turns blurry and nearly unreadable within minutes, with dots beside the lit ones flickering.

Dot matrix display goes blurry within minutes

Cause: The large square ASIC chip on the CPU board was making poor contact in its socket (seen on a Twilight Zone).

Checks

• Inspect the ASIC socket and pins.

Fix

• Remove the ASIC, clean its pins and reseat it.
• Also reseat the board ribbon cables.

Systems

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

Games

• Twilight Zone

Related tips

• DMD dead though display and controller work in other games: CPU board fault
• Blank display, garbage or diagonal lines: reseat ribbon cables
• Vertical lines and garbage on the DMD mid-game: press the ASIC back into its socket
• Moving vertical bars across the DMD with known-good display parts: CPU board fault
• Outhole, shooter diverter and gumball motor all dead: CPU board chip at U4
• Gumball diverter, popper and two bumpers dead in test: faulty CPU ribbon
• After a power cut: resets, then won't serve a ball
• "Country code must be specified" message

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