A 50 V coil does not fire on a game with relay boards under the playfield.

50 V coil dead on an early System 11 game

Cause: Cracked solder on the relay board, bad relay, coil fault, or a failed CPU driver.

Checks

• Briefly ground the coil lug and the relay board output to check the coil and its wiring.
• Briefly ground the relay board input and the TIP122 tab on the CPU board to see if the relay pulls in.
• Reflow and inspect the relay board solder joints, which commonly crack.

Fix

• Resolder the relay board; replace the relay or coil as needed.
• If grounding the driver tab fires the coil but the solenoid test does not, repair the CPU/driver board.

Systems

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

Related tips

• 50 V coils on early System 11: under-playfield relay boards
• System 11 coil outputs
• 50 V coils on earlier System 11 games
• Whole A or C bank of coils dead
• Slingshot or pop bumper will not fire (System 11)
• How the System 11 A/C bank select works
• How System 11 special solenoids work
• Which output drives the bank select relay

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