A single coil stays dead in the solenoid test.

One coil does nothing in the solenoid test

Cause: Burnt or open coil, broken lead at the coil, no +50 V (blown fuse or broken wire), or a failed driver transistor.

Checks

• Look at the coil for burning and check both wires are soldered firmly to the lugs.
• With the game on, briefly touch the coil lug that runs back to the driver (not the +50 V lug) to ground with a test lead.
• If the coil fires, briefly ground the tab (collector) of its driver transistor on the power driver board.
• If grounding the driver tab does nothing, check continuity from the transistor collector to the coil.

Fix

• Coil dead when grounded: restore +50 V (fuse, wire) or repair/replace an open coil; a broken winding near the lug can often be resoldered.
• Coil fires from the transistor tab but not in the test: the power driver board is at fault.
• Coil fires at the lug but not from the tab: repair the wiring between them.

Ground only for a moment; a held coil overheats.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)

Related tips

• One coil will not fire
• Firing each coil from the WPC solenoid test
• A coil does nothing although its fuse is good
• A solenoid will not fire in the solenoid test
• No coils work at all, fuses are good
• Press Start during the solenoid test for a coil's wiring details
• Coil-not-working checklist
• Left mini-playfield magnet dead, about 8 V at it: F101 blows, shorted Q26

Source: Pinball Machines: How They Work & Troubleshooting, Norbert Snicer