Random horizontal lines or garbage on the display (small displays may light completely), and no computer-controlled lamps, though the game plays.

DMD shows lines or lights up fully, and no CPU lamps work

Cause: The backbox 18 V lamp matrix fuse (8 A slow-blow, blue/white wire) has blown. On these games the display's +12 V is made from that 18 V circuit through CN5, not from the power supply's own 12 V, so the display crashes too.

Checks

• Check the backbox lamp matrix fuse.
• If it blows again, test the lamp matrix bridge and capacitor and look for a short in the lamp wiring.

Fix

• Replace the fuse after clearing any short.

Systems

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

Related tips

• Small and medium DMD power supply CN5 pinout
• DMD shows lines or garbage and no controlled lamps light
• Dot matrix shows lines or lights solid, and no CPU lamps work
• Every CPU-controlled lamp is out
• DMD power supply 520-5047 revisions by game
• Zener diodes D10 and D11 by DMD power supply revision
• Rebuild the high-voltage section of a 520-5047-00/-01/-02 supply
• Small display shows vertical lines

Source: Repairing DataEast 1987 (Laser War) to Sega 1995 (Batman Forever), Part Three, Clay Harrell (pinrepair.com)