The bottom two lines of the dot matrix display stay dark; the rest of the display works.

Bottom two rows of the DMD dark: row pins broken off the glass, bridged to the traces

Cause: Two of the row pins along the edge of the display glass had come away from their traces (one had already been patched with a jumper before).

Checks

• With the display out, inspect the pins along the glass edge with a magnifier for any that have lifted or cracked away from the traces.

Fix

• Very carefully grind away a little glass with a fine rotary-tool stone until a small part of the trace is exposed, then bridge the pin to it with solder or with conductive paint (the kind sold for rear-window defroster repairs), and secure the joint (hot glue was used by a member).
• If you are not comfortable working on the glass, replace the display.

The display runs on high voltage: unplug the game and let the supply discharge before removing it. Work slowly to avoid cracking the glass, and wear eye protection.

Systems

• Gottlieb System 3

Games

• Super Mario Bros.

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