The BEI Electronics II2D‑SB‑240‑AB‑7406R‑SMI6‑S is a high‑resolution incremental rotary encoder used in industrial servo drives and motion control systems. Common failure modes for this class include loss of signal or erratic output due to damaged contact pads, degraded optical track wear, EMI interference on the signal lines, or power supply ripple exceeding the encoder’s tolerance. Initial checks should verify that the 24 VDC supply is within spec and stable, inspect all wiring and connector pins for corrosion or breakage, and confirm that the encoder’s output signals (A/B channels) are clean square waves using an oscilloscope; also review any error codes from the host controller for communication faults.[oss-gpt-20b]