The game froze during play and would not finish a game, with LED 1 on the CPU board lit; earlier a ball stuck in a kickout hole because the 2.5 A solenoid fuse (F2) had blown.

Freezes mid-game and blows solenoid fuse F2: clean and reseat the 40-pin interconnect

Cause: Poor contact at the 40-pin interconnect between the CPU and driver boards. When the CPU locks up a solenoid can be left switched on, which then blows the solenoid fuse.

Checks

• Note whether the game froze just before the fuse blew.
• If the fuse keeps blowing even without freezes, measure the resistance of each coil; coils of the same type should read about the same.
• Check the flipper coil diodes.

Fix

• Reseat the 40-pin interconnect. If the problem returns, clean the pins with a fine wire brush; badly tarnished pins mean both halves of the connector should be replaced.

Unplug the game before removing or reseating board connectors.

Systems

• Williams System 4

Games

• Laser Ball

Related tips

• Double-solder the CPU board male header pins
• Replace the 40-pin interboard female connector
• Replace CPU board power connector 1J2
• Resolder the driver board header pins
• Always replace the driver board's 40-pin female interconnector
• Resolder and inspect the driver board header pins
• Making new interboard male pins long enough
• Removing the old interboard female connector

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