In the "All" lamps test, other lamps in a row or column (or a different one) come on, and the affected lamps stay lit about twice as long as the rest.

Lamps in a row or column light twice per sweep

Cause: A lamp socket diode has shorted, so a second row or column re-energises lamps that should be off.

Checks

• Watch the "All" lamps test for lamps that are on noticeably longer.
• Diode-test the socket diodes in the affected row or column.

Fix

• Replace the shorted 1N4004 lamp diode.

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
• One controlled lamp never lights, bulb is good
• Lamp lights twice or two lamps act as one
• Test a lamp socket diode in place
• Testing lamp-row drivers with a test lamp
• Testing lamp-column drivers with a test lamp
• Testing CPU switch rows and columns with a diode and clip lead
• Row or column fault on the playfield

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