During a game the backbox Match lamp comes on dim or bright, and all the player-count lamps light and pulse in time with playfield targets, though only one player is up.

Match and player lamps light at random in play: faulty replacement driver board

Cause: The newly fitted rebuilt driver board was faulty in its lamp circuits. With the original driver board back in, the lamps behaved normally.

Checks

• Remove the affected backbox bulbs and look for a worn or broken insulating disk shorting inside the socket.
• If the sockets are fine, swap the driver board to see if the fault follows the board.

Fix

• Repair or replace the faulty driver board.

Systems

• Williams System 6 / 6A

Games

• Gorgar

Related tips

• Some lamp columns over-bright: board or playfield?
• Light a lamp row by grounding its transistor
• Diode-test the lamp pre-drivers (2N6427/MPSA14)
• Photo: MOSFET lamp drivers with jumper wires
• A whole lamp row or column dead or stuck on
• Background sound never stops at game over: sound-line driver chip
• Kicker coil locks on again after a new TIP122: dead 7408 gate on the driver board
• How the lamp matrix runs 6.3 V bulbs on 18 V

Source: Pinball Repair help group!! (Facebook group)