Part of the lamp matrix is dead or erratic, but the row and column transistors test good.

Lamp matrix fault with good transistors: check R55 to R62

Cause: One of the eight 0.4 ohm, 3 W wirewound resistors (R55 to R62, lower right of the CPU board) has run hot and unsoldered itself or dropped off.

Checks

• Inspect R55 to R62 for cracked joints or missing parts.
• Measure each resistor.

Fix

• Resolder or replace the resistor, ideally standing it slightly off the board.

Systems

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

Related tips

• Lamp row still dead after a new TIP122
• Lamp column still dead after a new TIP42
• Quick lamp row check: ground the row transistor tab
• Test each lamp column driver with a test lamp
• Test each lamp row 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
• Lamps glow dimly when they should be off

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