One of the two right stand-up targets shows closed all the time in switch test and never scores; hitting the other one also triggers it. Wiring, diodes and the MPU PIA had all been checked.

Stand-up target always closed in test and ghosting another: failed switch capacitor

Cause: The original small disc capacitor across the target switch had failed (they degrade with age), shorting the switch.

Checks

• Temporarily unsolder one leg of the capacitor on the suspect switch: if the fault disappears, the capacitor is bad.
• Check the other switch capacitors on the game; the originals are all the same age.

Fix

• Replace the failed capacitor (and ideally the other original switch capacitors) rather than leaving it off, since fast ball hits may not register without it.

Systems

• Bally MPU AS-2518-35

Games

• Flash Gordon

Related tips

• Rollover switch only registers with two diodes fitted: failing PIA at U10
• Slingshot switch causes a tilt, or PIA chips fail
• Hitting switches in one matrix row tilts the game: bad capacitor on the tilt bob
• Switch reads stuck closed, or a pop bumper chatters
• One switch or a string of switches never registers
• Random game faults when a switch without a diode sticks
• Pop bumper and both outkicker switches dead: bare wire touching the coin door
• Switch matrix confused by a bad MPU DIP switch diode

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