The 2.5 A solenoid fuse blows soon after replacement, especially once the slingshots and pop bumper start firing.

2.5 A solenoid fuse keeps blowing: check it is a slow-blow fuse

Cause: A fast-acting fuse had been fitted where the game calls for a 2.5 A slow-blow (time delay) fuse.

Checks

• Read the fuse type, not just the rating, and compare with the manual.
• If the correct fuse still blows, check the special solenoid coils' resistance and diodes, and whether the fuse survives with the special solenoid switch plug unplugged.

Fix

• Fit a 2.5 A slow-blow fuse.

Systems

• Williams System 7

Games

• Black Knight

Related tips

• Solenoid fuse blows as soon as the game is turned on
• Solenoid fuse F2 blows at power-up as every coil fires: CPU blanking circuit
• Solenoid fuse blows: check the coin lockout coil
• Wires to a few upper playfield lamps get hot and melt: bent lamp socket tab
• Switch matrix chip and PIA keep failing: coil voltage leaking into the matrix

Source: Pinball Repair help group!! (Facebook group)