A pop bumper or sling coil stays energized until a fuse blows or the coil cooks.

Pop bumper or slingshot locked on

Cause: Special solenoids are not one-shot: a stuck-closed trigger switch, or a shorted resistor or capacitor across it, holds the coil on. Even briefly locked-on pops often take out the driver transistor, and sometimes the gate chips and PIA.

Checks

• Check the playfield trigger switch for welded or bent contacts.
• Check the 22 MFD capacitor and 100 ohm resistor across the switch for shorts.
• Check the coil diode.

Fix

• As a first test, cut one lead of the resistor at its lug to take the RC parts out; the device still works without them.
• Fix the switch, replace the shorted parts and reconnect or replace the resistor and capacitor afterwards.
• Test and replace the driver transistor and pre-driver if they were damaged.

Systems

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

Related tips

• Pop or sling works in the game but not in test, or the reverse
• Coil outputs available on System 3-7
• The coin lockout coil is meant to be on
• Check the wire from the coil to its driver transistor
• A cracked coil diode keeps killing its driver transistor
• Solenoid driver test at 2J9 and 2J11 with Leon's code
• Special solenoid trigger test at 2J12/2J13
• CPU-controlled and special solenoids

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