Some controlled lamps glow faintly when they should be off; the lamp test shows two neighbouring columns acting together.

Lamps glow dimly when they should be off

Cause: The metal tabs of two adjacent lamp driver transistors on the CPU board are touching and shorting their outputs.

Checks

• Unplug the lamp connector: if the short between the two lines goes away, look at the board.
• Check the transistor tabs next to each other for contact.

Fix

• Bend the transistor tabs apart so they cannot touch.

Systems

• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b

Related tips

• Test each lamp column driver with a test lamp
• How the CPU-controlled lamp matrix is wired
• A whole row or column of lamps is stuck on and extra bright
• Lamp column still dead after a new TIP42
• Lamp matrix fault with good transistors: check R55 to R62
• Test each lamp row driver with a test lamp
• Check the lamp matrix outputs with a logic probe
• Quick lamp row check: ground the row transistor tab

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