In the display test, the entire top and bottom rows and the left and right columns of the dot matrix display stay dark, forming a dead frame around a working centre. New display controller chips and a new ribbon cable make no difference.

Whole outer frame of DMD dots dead: pins snapped off the display glass

Cause: The fine wire pins that connect the glass panel to its board had snapped at the ends of the display, usually from flexing and rough handling or nudging over the years.

Checks

• Remove the DMD and inspect the pins along the edges of the glass where it meets its board.
• If possible, try the display in another game or with an all-dots-on test to rule out the controller board and cable.

Fix

• Replace the DMD panel; the glass-to-board connections are bonded and are not practical to repair.

Plasma DMDs run on high voltage (around 100 V and more); power off and let the supply discharge before handling the display or its board.

Systems

• Data East CPU Version 3
• Data East/Sega CPU Version 3b

Related tips

• DMD keeps resetting in attract mode: torn ribbon cable at the display controller
• DMD shows random garbage after reassembly: failed display driver board
• Dot matrix controller CPUs by display size
• Display not working: check +5 V at the controller first
• Checklist for a dead small or medium dot matrix display
• Dot matrix display goes blank after a few minutes
• Black DMD: Data East DMD controller has no clock past the 74HCT240 at U1
• DMD shows lines or garbage and no controlled lamps light

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