The coil fires when grounded and its wire reaches the driver board, but the game cannot fire it (or it stays on).

Coil has power and wiring is good but still dead or locked on

Cause: The driver transistor, its 7408 gate or the IC5 solenoid PIA. A pop or sling may simply have a stuck trigger switch.

Checks

• Rule out a stuck special solenoid trigger switch.
• Diode-test the TIP and 2N4401, then the gate chip, then logic-probe the PIA.

Fix

• Resolder the driver board header pins first, then replace the failed parts.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A
• Williams System 7

Related tips

• Coil still locked on with good transistors and gate
• Spare transistors for driver board and power supply
• Solenoid fuse blows at power-on and solenoids fire: driver board logic chips
• A low resistance coil points to a bad driver transistor
• All coils or lamps lock on at power-up
• One or a few coils lock on at power-up
• Kicker coil locks on again after a new TIP122: dead 7408 gate on the driver board
• Nearly every coil energizes at power-on

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)