The coil, driver and pre-driver all test good and the coil fires when its driver tab is grounded, but it does not work in play.

Coil fires when tested but not in game play: TTL driver chip

Cause: The 7408 (standard solenoids) or 7402 (special solenoids) logic chip feeding that driver pair has failed.

Checks

• U17 (7408) feeds drivers Q6, Q7, Q14 and Q15 (pre-drivers Q2, Q3, Q10, Q11).
• U18 (7408) feeds drivers Q8, Q9, Q16 and Q17 (pre-drivers Q4, Q5, Q12, Q13).
• U19 (7408) feeds drivers Q22, Q23, Q30 and Q31 (pre-drivers Q18, Q19, Q26, Q27).
• U20 (7408) feeds drivers Q24, Q25, Q32 and Q33 (pre-drivers Q20, Q21, Q28, Q29).
• U45 (7402) feeds special solenoid drivers Q69, Q71, Q73 and Q75 (pre-drivers Q68, Q70, Q72, Q74).
• U50 (7402) feeds special solenoid drivers Q77 and Q79 (pre-drivers Q76, Q78).
• Check the chip outputs with a logic probe while the coil should fire.

Fix

• Replace the chip that drives the failed pair, fitting a socket.

Systems

• Williams System 11
• Williams System 11A
• Williams System 11B
• Williams System 11C

Related tips

• How a coil or flasher is switched: PIA to TTL to pre-driver to driver
• A coil or flasher comes on and stays on at power-up
• Damage after the black and white plugs were swapped
• Diverter coils dead and flippers live at game over: 7402 at U50
• Right sling locks on at power-up and a pop is dead: bad 7402 at U45
• 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
• Flippers and special coils all dead

Source: Repairing Williams System 11 Pinball 1986 to 1990, Deel 1, Clay Harrell (pinrepair.com)