Display test shows a strange error pattern, and when the video mini-game starts on the dot matrix the game restarts until it ends. 5 V is fine.

Display test shows errors and the DMD mini-game restarts the game: faulty DMD

Cause: The dot matrix display panel itself was faulty, even though it seemed to work at first in another game.

Checks

• Swap in a known good DMD panel from another game before replacing RAM, cables or the controller.
• Test the suspect panel in another game for longer, including its mini-game or animation-heavy scenes.

Fix

• Replace the dot matrix display.

DMD panels use high voltage; switch off before unplugging.

Systems

• Gottlieb System 3

Games

• Cue Ball Wizard

Related tips

• Display works in a Williams game but not in System 3
• System 3 games with 128x32 dot matrix displays
• Bottom two rows of the DMD dark: row pins broken off the glass, bridged to the traces
• Dot matrix dark: +62 V missing
• Garbage on the dot matrix at power-on
• The A8 dot matrix controller board
• DMD controller LED stays on

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