When the gold ball comes into play the diverter flap to its trough opens as normal, but it closes again part-way through play, so when the gold ball drains both balls end up in the normal trough.

Gold ball and play ball both end up in the normal trough: gold ball switch wire bent

Cause: The actuator wire on the gold ball microswitch (probably not the original) was bent so the switch triggered too early.

Checks

• Watch the gold ball switch in switch test as the ball rolls over it.
• Check the transistor that drives the diverter and the wiring and connectors in between.

Fix

• Bend or replace the microswitch actuator wire so the switch only closes when the gold ball reaches it.

Systems

• Bally MPU AS-2518-35

Games

• Gold Ball

Related tips

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• Vector: trough switches
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• Game drops back to attract mode a minute into play: ball trough switch stuck closed

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