The knocker coil stays energised although its drive transistor tests good out of the board.

Knocker coil energised but transistor tests good: broken trace from socketing

Cause: During an earlier repair, socketing the chips had broken the trace between U19 pin 12 and U28 pin 15 on the CPU board.

Checks

• Check continuity along the knocker's logic path between the chips that feed its driver.
• Also check the coil's wiring is not chafed to ground.

Fix

• Repair the broken trace with a jumper wire.

Systems

• Williams System 11A

Games

• F-14 Tomcat

Related tips

• Outhole kicker dead after moving the game: broken wire at the coil diode board
• A group of coils won't fire but fire when grounded: wire off the flipper board connector
• Both left flippers lose power: broken solder joint on the upper flipper coil

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