A loud crack, then a group of feature lamps stops working; a 2N5060 SCR on the CPU board is split open.

Lamp driver SCR blew apart with a crack

Cause: A lamp socket lug touched a coil lug under the playfield, sending coil voltage into the lamp circuit. Some sockets sit very close to coil terminals.

Checks

• Look under the playfield for lamp socket lugs touching or nearly touching coil lugs, often at drop target or other coils.

Fix

• Bend the socket clear or insulate it, then replace the blown 2N5060 on the CPU board.

Systems

• Bally 6803

Related tips

• An LED stays dark on a lamp header during the test
• Test a 2N5060 lamp matrix SCR with a meter
• Lamp driver board layout: SCRs, decoders and connectors
• Lamp and switch matrix transistor positions on the CPU board
• How 6803 feature lamps share SCR drivers
• Lamp row still dead after a new TIP122
• Lamp matrix still wrong after replacing transistors: upstream parts
• Some feature lamps out after the backbox was lowered

Source: Repairing Bally 6803 Pinball Games from 1985 to 1989, Clay Harrell (pinrepair.com)