A segment is missing or stuck on and the display board checks out.

Segments missing or stuck on: CPU board PIAs 9B and 7B

Cause: The PIA at 9B (sometimes 7B) on the CPU board, or the 4.7k networks RA21, RA22 and RA23 it drives.

Checks

• With power off, measure each RA network from its pin 1 to the other pins: all should read the same (4.7k or 2.5k). A bad PIA can make an RA look bad.
• Diode test each PIA pin with the red probe on ground: 0.4 to 0.6 V on all pins except 1, 20, 22, 24 and 40.
• PIA 9B can be pulled and the game will still boot with a mostly blank display; if a stuck segment goes away, 9B was the cause. 7B cannot be tested this way.

Fix

• Replace the bad PIA or resistor network.

Systems

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

Related tips

• CPU board PIA positions and jobs
• Switch column (drive) circuit on the CPU board
• How a coil or flasher is switched: PIA to TTL to pre-driver to driver
• One PIA output does not toggle under the test EPROM
• Lamp column still dead after a new TIP42
• A coil or flasher comes on and stays on at power-up
• Which logic chips drive which solenoid transistor pairs
• Test EPROM flash codes: which chip failed

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