Pressing start shows "ball missing" although all three balls are in the trough, or extra balls are fed to the shooter lane.

"Ball missing" with all balls in the trough

Cause: Light from nearby playfield lamps (the RAIN feature lamps on Blackwater 100) leaks into the trough and fools the opto receivers.

Checks

• Use the switch test to confirm every trough receiver changes state with a ball.

Fix

• Remove the bottom arch plate and cover the trough walls with black cardboard, duct tape or other opaque material, taped in place.

Systems

• Bally 6803

Games

• Blackwater 100
• Dungeons & Dragons

Related tips

• Ball missing or balls stacking in the shooter lane
• Get at the trough opto boards for testing
• Trough opto numbering is backwards
• Dungeons & Dragons and Blackwater 100 use trough optos
• Test trough emitters and receivers
• NTE replacement emitters fit the opposite way round

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