After routine work on the game, three columns of dots are missing on the dot matrix display; reseating the cables does not help.

Three vertical lines missing on the DMD: glass cracked by a mounting screw

Cause: A screw holding the display had cracked the edge of the glass, breaking the leads for those columns.

Checks

• Swap the display into another game of the same generation: if the lines stay missing, the display itself is at fault.
• Look closely at the glass edges and the pins where the leads leave the glass, especially near screws and pins that get pushed when the backglass is removed. Pressing lightly on that area may bring the lines back if pins are cracked.

Fix

• Replace the display (or an LCD/colour replacement). A careful owner can sometimes expose the broken lead and solder a jumper, but a cracked glass is usually the end of that display.

The DMD runs on high voltage: unplug the game before touching the display or its cables.

Systems

• Sega/Stern Whitestar

Games

• NFL

Related tips

• DMD shows the boot image then goes blank while the game plays: replace U201
• DMD stays dark while the game plays music: 74HCT240 on the display controller
• Display stuck on the audit screen while the game runs: acid damage on the DMD controller

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