After U20 failed and was replaced, the game played but the DMD showed stuck garbage or nothing. The DMD and its controller both worked in other games, and other games' controllers wouldn't even let this game boot. Voltages at the display were fine and new ribbon cables changed nothing.

DMD dead though display and controller work in other games: CPU board fault

Cause: A fault on the CPU board (the same event that killed U20), not the display or its controller.

Checks

• Swap the DMD and DMD controller into a known good game to clear them.
• Fit new ribbon cables and check orientation.
• Try a known good CPU board.

Fix

• Repair or replace the CPU board.

Systems

• WPC Fliptronics

Games

• Twilight Zone

Related tips

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

Source: Pinball Repair help group!! (Facebook group)