During a game vertical lines appeared on the dot matrix display, followed by garbled graphics. Swapping in another display didn't help, and reseating connectors helped only for a few minutes.

Vertical lines and garbage on the DMD mid-game: press the ASIC back into its socket

Cause: The large square ASIC chip on the CPU board had crept up in its socket and was making poor contact, which corrupts the display data.

Checks

• Run the display test all the way through and note any RAM error; a flaky ASIC socket or ribbon cable can cause that message too.
• Reseat or replace the ribbon cable between the CPU and the display controller; old original cables often fail.

Fix

• With the game off, take out the CPU board, lay it flat on a piece of cardboard and press firmly on the ASIC with both thumbs until it seats fully in its socket. Refit the board and run the display test again.

Switch the game off before removing the CPU board; the display high-voltage board behind the DMD carries dangerous voltages.

Systems

• WPC Fliptronics

Games

• Bram Stoker's Dracula

Related tips

• Blank display, garbage or diagonal lines: reseat ribbon cables
• Moving vertical bars across the DMD with known-good display parts: CPU board fault
• Dot matrix display power connector pinout and voltages
• Resets caused by a failing dot matrix display
• Dot matrix display faults
• Dot matrix display goes blurry within minutes
• Dot matrix display supply voltages
• Dot matrix display blank or faulty

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