Weko 7908 is a compact optical photoelectric sensor commonly mounted on conveyor or pick‑and‑place lines for presence detection and position feedback. Known failure modes for this class include misalignment of the emitter/receiver pair, contamination of the sensing window, LED degradation due to over‑voltage or thermal stress, and PCB solder joint fatigue from vibration. Begin troubleshooting by verifying power supply voltage and polarity at the sensor terminals, inspecting the optical window for dirt or damage, and checking the output signal with a multimeter or oscilloscope against expected logic levels; if the unit remains unresponsive, examine the internal LED and photodiode connections for shorts or opens.[oss-gpt-20b]