FU1 (5 A slow-blow) blows instantly at power-on.

Coil fuse FU1 blows the moment the game is switched on

Cause: The coil bridge rectifier BR1 (35 A 200 V) has shorted; less often the varistor VA1 shorted, usually from high line voltage.

Checks

• Test BR1 with the meter on diode setting.
• Check VA1 for a short.
• Check R1 (600 ohm 10 W): it should be within 10% and not open.

Fix

• Replace BR1 or VA1 as found, then fit a new 5 A slow-blow FU1.

Unplug the game before pulling fuses or working on the power supply; the transformer side carries line voltage.

Systems

• Bally 6803

Related tips

• Check every power supply fuse before first power-up
• 6803 power supply fuse ratings
• High-voltage input fuse FU2 blows
• Power supply test points and their voltages
• No 43 V for the coils
• Power supply test point ranges
• Bad +5 V bridge diodes D1-D4
• Missing lamp fuse changes the flash count

Source: Repairing Bally 6803 Pinball Games from 1985 to 1989, Clay Harrell (pinrepair.com)