An opto switch misses or chatters.

Opto switch intermittent

Cause: Cold solder joints on the opto emitter or receiver.

Checks

• Inspect the joints on both opto parts.

Fix

• Reflow fresh solder on both joints of both optos.

Systems

• Gottlieb System 3

Related tips

• Keep opto switches clear

Source: Repairing Gottlieb System 3 Electronic Pinball Games from 1989 to 1996, Clay Harrell (pinrepair.com)