How WPC opto switches work and which half fails

An opto switch is an infrared LED transmitter facing a photo transistor receiver. The transmitter is lit the whole time the game is on, so it is the half that burns out in nearly every failure; the receiver rarely dies. A blocked beam reads as an open switch. On stand-up optos the transmitter usually sits in a white case on a small green board and the receiver in a black case on a small blue board.

Systems

• WPC Alpha-Numeric
• WPC Dot Matrix
• WPC Fliptronics
• WPC DCS
• WPC-Security (WPC-S)
• WPC-95

Related tips

• Where WPC games use opto switches
• Some WPC-95 optos can fail even when they test good
• Testing optos in switch edge test
• Flipper cabinet opto switch boards
• Opto switches dead or intermittent: check the 12 volt supplies
• Opto switches dead all at once
• Opto does not work: check 12 V at the transmitter connector
• WPC-95 five-leg Schmitt trigger U optos

Source: Repairing Williams/Bally WPC Pinball Games from 1990 to 1999, Part Three, Clay Harrell (pinrepair.com)