Fast-blow fuse F4 blows, sometimes instantly at power-on.
Main solenoid fuse F4 blows (hard short)
Cause: A hard short: a coil under 2 ohms, a shorted coil diode, coil power touching ground, the backbox knocker, the coin lockout coil, the solenoid bridge rectifier or the rectifier board varistor. (A coil that stays energized usually blows the 1 A playfield fuse instead.)
Checks
- Unplug rectifier board J1 and J3, fit a new F4 and power up. If it still blows, the solenoid bridge or the varistor is bad.
- If it holds, reconnect, then disconnect one wire on each coil and reattach them one at a time until F4 blows to find the coil, diode or driver at fault.
Fix
- Replace the shorted part.
Systems
Related tips
- F3, F4 or F5 blows on the rectifier board
- Use a standard 3AG fuse in place of the short 8AG HV fuse
- Rectifier board and playfield fuse ratings
- Which rectifier to suspect for each blown fuse
- Hot, discoloured fuse clips
- Finding a short that blows GI fuse F5
- Find a short that blows the 20 A GI fuse
- Solenoid fuse blows even with the outputs unplugged: fault on the rectifier board
Source: Repairing Bally Electronic Pinball Games from 1977 to 1985, Part Three, Clay Harrell (pinrepair.com)