The playfield or backbox lamp fuse blows.

6 V lamp fuse keeps blowing

Cause: A lamp socket's centre tab bent onto its shell (often on sockets at the playfield edge), something metal dropped in a socket, a lamp wire touching the frame, a shorted bulb (including #455 flashers), or a short at a connector.

Checks

• Fit a circuit breaker in place of the fuse.
• Remove all bulbs; if the breaker stops tripping, refit them one at a time to find the shorted one.
• If it still trips, cut the lamp feed where it enters the playfield, then reconnect a section at a time until it trips.
• Inspect every socket for bent tabs and debris.

Fix

• Straighten or replace the shorted socket, reinsulate the wire, or replace the bulb.

Systems

• Electro-mechanical

Related tips

• Playfield lamp fuse blows when one pop bumper fires: lamp socket shorting
• Repair a loose playfield lamp socket
• Lamp types found in EM games
• Bally lamp sockets are the weakest
• Gottlieb: lamps dim noticeably each time a coil fires
• Gottlieb feature lamp burns out after switching to high tap
• Dim or flickering lamp sockets
• Change pop bumper lamp sockets from wedge to #47 bayonet

Source: Repairing Electro-Mechanical (EM) Coin Operated Games to 1978, Part One, Clay Harrell (pinrepair.com)