The game resets or locks up at random.

Random resets and lock-ups from the +5 V filter cap

Cause: The main +5 V filter capacitor C1 (11,000 mfd) on the power supply has dried out; these last roughly ten years.

Checks

• With the game on, set the meter to low AC volts and measure across C1's terminals; after it settles it should read 0.25 VAC or less.

Fix

• Replace C1 with an 11,000 mfd axial cap. It is worth doing on every 6803 game.

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

Systems

• Bally 6803

Related tips

• Missing lamp fuse changes the flash count
• CPU LED stops just short of the full count
• Replace high-voltage caps C6 and C7 before they take out Q2/Q3
• Strange intermittent faults from power supply solder joints
• Where the boards sit in a 6803 backbox
• 6803 power supply fuse ratings
• Check every power supply fuse before first power-up
• Power supply test points and their voltages

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