After fitting new capacitors across the stand-up target switches (to help them register), one target scores continuously as soon as its capacitor is connected, even with a brand-new capacitor.

Stand-up target scores over and over once its capacitor is fitted: bad switch diode

Cause: That switch's isolation diode was faulty. Without a working diode the capacitor charges on every column strobe and the game reads it as a switch closure. The diode still tested good on the bench.

Checks

• Compare the faulty switch with a good one: on the good ones, bridging the diode with meter leads in-game registers the switch; if the odd one behaves differently, suspect its diode.
• Use ceramic capacitors of the value in the manual, not tantalum ones.

Fix

• Replace the switch diode even if it tests good out of circuit, then refit the capacitor.

Games

• Trident

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