The dot matrix display is sometimes completely garbled and unreadable, then fine again for hours.

Display intermittently garbled after new driver board and cables: the DMD itself

Cause: The dot matrix display panel itself was failing.

Checks

• Swap the ribbon cables with known-good ones.
• Check the display voltages at the driver board test points and at the display connector, including both high-voltage supplies, while the fault is showing.
• Reflow the high-voltage section of the driver board if its joints look tired.
• Try a known-good display.

Fix

• Replace the dot matrix display (or fit an LED replacement display).

The DMD supplies run at over 100 V; take readings carefully and keep fingers off the display power section with the game on.

Systems

• WPC DCS

Games

• Red & Ted's Road Show

Related tips

• Dot matrix display faults
• Display shows garbage or nothing though the glass is fine
• Blank display, garbage or diagonal lines: reseat ribbon cables
• Dot matrix display supply voltages
• Which dot matrix displays fit WPC games
• Dot matrix display goes blurry within minutes
• DMD fully lit with no picture while the game plays: bad DMD panel
• Dot matrix display blank or faulty

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