A pop bumper, slingshot or kickback fires rapidly over and over, or stays energized and gets hot; its fuse may blow.

Pop bumper or slingshot machine-guns or locks on (Fire! and earlier)

Cause: The direct-fire special switch for that coil is stuck closed, so the driver keeps firing without the CPU limiting it.

Checks

• Turn the game off at once if the coil is hot or smoking.
• Find the special switch for that coil (these feed CPU connector 1J18) and check whether it is closed at rest.

Fix

• Clean, re-gap or replace the stuck switch.
• Check the coil and its fuse for damage before powering up again.

Systems

• Williams System 11
• Williams System 11A

Related tips

• Special solenoids dead after fitting an early System 11 CPU in a later game
• Lizard eye flashers locked on, then not flashing: bad drive parts and a missing resistor
• How System 11 A/C switched solenoids work
• Controlled solenoids 9-16
• No plug at CPU 1J18 means CPU-controlled special solenoids
• Which transistor drives the A/C select relay
• Whole groups of coils or all flashers dead: A/C select relay stuck
• Right sling locks on at power-up and a pop is dead: bad 7402 at U45

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