FU2 (high voltage in) is blown and the score displays are dark.

High-voltage input fuse FU2 blows

Cause: A shorted rectifier diode in D5-D8.

Checks

• Test D5-D8 (1N4004) with the meter on diode setting.

Fix

• Replace the shorted diode and fit a new 3/4 A fast-blow FU2.

The display supply runs at 170-230 volts DC; touch nothing on the high-voltage section with the game on, and let it discharge before working on it.

Systems

• Bally 6803

Related tips

• No score displays light at all
• Rebuild the solenoid driver board high-voltage section
• System 80B alphanumeric displays dark: check the display board supply
• Score displays dead or dim: high-voltage section parts
• Fliptronics flipper coil wired wrongly
• Rebuild the high-voltage display supply
• Game locks up or behaves strangely, worst in multiball
• Test the switch row inputs with a diode jumper

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