Testing an opto receiver

Steps

• Put the game in switch edge test.
• Cover the transmitter with black electrical tape.
• Shine a penlight or a TV remote into the receiver: the switch should close (solid block changes to a small dot) and open again when the light is removed.
• Meter method: black lead on ground (the side rail works). With the transmitter taped over, one receiver leg (gray wire) reads 12 V DC and the other (orange wire) near 0 V.
• Keep the red lead on the low leg and shine a light in: it should rise to about 12 V and drop back when the light goes away.
• No change, or 12 V on both legs with no stray light falling on it, means the receiver is bad. If the receiver passes but the switch still fails, the transmitter is the likely culprit.

Systems

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

Related tips

• Mounting a replacement opto receiver
• Telling an opto transmitter from a receiver
• Replacement opto transmitter and receiver pinouts
• Replacement opto receiver dead or weak: try it with the notch the other way
• Opto parts to keep on hand
• Opto styles used in WPC games
• Cleaning dusty optos
• Testing optos in switch edge test

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