Targets drop but do not score, or the bank does not reset when all are down.

Drop targets stop scoring or the bank will not reset

Cause: Switch diodes or capacitors vibrated loose, dirty wiper contacts, or broken or missing daisy-chain jumper wires between the target boards.

Checks

• Check the diodes and capacitors on the bank.
• Check every jumper wire on the back of the boards and its solder joints.

Fix

• Refit diodes and caps with short leads and secure them with hot glue or silicone.
• Replace or resolder the jumper wires.
• Expect to clean these banks every six months to a year even in home use.

Systems

• Williams System 3
• Williams System 4
• Williams System 6 / 6A

Related tips

• Testing a System 3-6 drop target bank
• System 3-6 drop targets use two switches per target
• Cleaning and rebuilding System 3-6 drop targets
• Stand-in for a broken drop target wiper
• Drop targets will not reset or stay up

Source: Repairing Williams System 3 to System 7 Pinball 1977 to 1984, Part Three, Clay Harrell (pinrepair.com)