The game will not start because a ball is missing, or two or three balls are fed into the shooter lane at once.

Ball missing or balls stacking in the shooter lane

Cause: Bad solder joints or bad 68 ohm resistors on the trough opto boards, or failing optos.

Checks

• Check each 68 ohm resistor on the trough boards.
• Check the opto states in the switch test.

Fix

• Remove the old solder, clean the pads (the boards are single-sided) and resolder; replace bad resistors or optos.

Systems

• Bally 6803

Games

• Blackwater 100
• Dungeons & Dragons

Related tips

• "Ball missing" with all balls in the trough
• Trough opto numbering is backwards
• Get at the trough opto boards for testing
• Test trough emitters and receivers
• Stop trough optos from breaking with vibration

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