One lamp does not light, or is dim or flickers.

Single lamp out, dim or flickering

Cause: A burned-out bulb, a broken socket wire, or a dirty, corroded or loose socket.

Checks

• Try a known-good bulb; recessed backbox bulbs come out easily with an old rubber shooter tip or a short piece of 5/16 in inside-diameter tubing.
• Check the socket wires for breaks or unsoldered joints.

Fix

• Clean the socket contact with a pencil eraser or a socket cleaning stick, and clean the bulb base.
• On old EM sockets with a spring inside, pull the spring out with fine pliers to clean and stretch it.
• Squeeze a loose bayonet socket very slightly so it grips the bulb.
• If the socket is worn out, replace it.

Switch the game off before working on sockets with pliers; a slip can blow a fuse or burn out many bulbs at once. Do not twist a loosely mounted socket, which can short its wires.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7
• Williams System 9
• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C
• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95
• Bally MPU AS-2518-17
• Bally MPU AS-2518-35
• Stern MPU-100
• Stern MPU-200
• Bally 6803
• Gottlieb System 1
• Gottlieb System 80
• Gottlieb System 80A
• Gottlieb System 80B
• Gottlieb System 3
• Data East CPU Version 1/2
• Data East CPU Version 3
• Data East/Sega CPU Version 3b
• Capcom
• Electro-mechanical

Related tips

• Lamp flickers or is out with a good bulb
• A single controlled lamp out
• One controlled lamp does not light
• A single lamp does not light
• A single lamp is out: the usual causes
• Dim or flickering lamp sockets
• LED replacement lamps
• One controlled lamp out while the rest of the matrix works

Source: Pinball Machine Care & Maintenance, Bernard B. Kamoroff (Bell Springs Pinball Alley)