Add fuses to the +25 V solenoid and +18 V lamp bridges (Fire! and earlier)

Steps

• Turn the game off and unplug it.
• Find the two bridge rectifiers on the inside right of the backbox, above the large 30,000 mfd capacitor: one for the +25 V solenoid supply and one for the +18 V lamp matrix.
• On each bridge, remove the wire from a terminal marked AC (either one if both are marked).
• Connect that wire to one side of a new fuse block and run a wire from the other side of the block back to the bridge AC terminal.
• Fit an 8 A slow-blow fuse in each block and label each block with its rating and type.

These two supplies have no fuse from the factory; a shorted bridge or filter capacitor can start a fire. Work with the game unplugged.

Systems

• Williams System 11
• Williams System 11A

Related tips

• Half the backbox lamps and the lower displays dead: check the backbox fuses
• Cannons and VUK never fire, even in coil test: check every driver board fuse
• Testing fuses with a meter
• Special solenoid fuse blows at power-up: a pop bumper switch held closed
• Common fuse ratings to stock
• Fuse ratings to stock for System 11
• Interconnect board and flipper power board fuses
• Check every fuse for the right rating and type before power-on

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