The drop targets intermittently fail to score when knocked down.

Drop targets sometimes don't score: worn horseshoe contacts

Cause: The horseshoe contact blades in the drop target switch assemblies were broken and worn. Each target has a momentary contact that scores as it drops and a second contact that stays closed at the bottom.

Checks

• Take the small switch boards off the targets and inspect the horseshoe blades.
• If targets fail to score, look at the momentary contact; if they fail to reset, look at the bottom contact.
• Clean the board traces and check the diodes and wiring for cracked joints.

Fix

• Replace the horseshoe contacts (left and right hand versions differ), clean the traces with isopropyl alcohol, and make sure the targets slide freely.

Systems

• Williams System 6 / 6A

Games

• Tri Zone

Related tips

• A drop target switch registers when the lower pop fires: replace the pop coil
• Hitting a pop bumper resets the drop targets: faulty pop bumper coil

Source: Pinball Repair help group!! (Facebook group)