Replacement opto transmitter and receiver pinouts

The transmitter is industry part QED123 (5 mm infrared LED). Its flat side and shorter lead is the cathode K, which normally takes the black switch matrix wire; the gray wire goes to the anode A. The receiver is QSD124 (5 mm photo transistor, usually black). Its flat side and shorter lead is the emitter E, which takes the orange wire; the gray wire goes to the collector C.

Systems

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

Related tips

• Telling an opto transmitter from a receiver
• Testing an opto receiver
• Replacement opto receiver dead or weak: try it with the notch the other way
• Bookcase opto still dead after a new receiver: the replacement part was bad
• Optos test good but still don't work: the opto board
• Opto does not work: check 12 V at the transmitter connector
• Replacement five-leg U slot opto (WPC-95)
• Fitting a replacement U slot opto the right way round

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