A coil fuse blows at power-on.

Solenoid fuse blows as soon as the game is turned on

Cause: A pop bumper or slingshot switch stuck closed holding its coil on, a shorted coil (under 2.5 ohms), usually from a shorted driver transistor, or a short from coil voltage to ground.

Checks

• Look for closed pop bumper and slingshot activation switches.
• With the game off, measure every coil; each should be 2.5 ohms or more.
• Disconnect the return wire from any low coil and power up with a new fuse to see if it still blows.

Fix

• Gap or replace stuck activation switches.
• Replace shorted coils, then find and replace the shorted driver transistor that burnt them.

Systems

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

Related tips

• Solenoid fuse blows: check the coin lockout coil
• Pull the coil and lamp fuses for the first power-up
• 2.5 A solenoid fuse keeps blowing: check it is a slow-blow fuse
• Solenoid fuse blows at power-on: frayed 28 V wire touching ground under the playfield
• Fuse blows again right away
• System 3 fuse chart
• System 4 fuse chart
• System 6 fuse chart

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