One playfield or backbox lamp does not light.

A single lamp is out: the usual causes

Cause: Most often a dead bulb, then a wire broken off the socket lug, a diode loose from the socket, or a corroded socket (common on games brought back from abroad).

Checks

• Check the bulb for continuity with the meter.
• Look for a wire or diode lead broken off the socket.
• Re-seat the bulb and look for corrosion.

Fix

• Replace the bulb, resolder the wire or diode, or clean or replace the socket. For plug-in 555 sockets, ease the outer tabs outward a little.

Systems

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

Related tips

• Lamps on a plug-in lamp board do not light
• One controlled lamp never lights, bulb is good
• Single lamp out, dim or flickering
• Every CPU-controlled lamp is out
• Two lamps flash together in the single lamp test
• Star Trek and Hook ramp chase lights do not run
• Lamps in a row or column light twice per sweep
• Test each lamp column driver with a test lamp

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