The Fanuc A20B‑1001‑0770 is a triple‑axis AC servo drive control PCB used on the 6050 series drives; it functions as an analog velocity‑control unit that interfaces with incremental encoders and the CNC controller. Common failure points include burned or cracked capacitors on the power supply section, damaged signal traces between the three channel outputs, and degradation of the encoder interface ICs due to vibration or overcurrent. Initial checks should verify proper 48 V input voltage and polarity, inspect for visual signs of component damage (burn marks, bulging caps), and confirm that each channel’s output signals match expected waveforms using an oscilloscope; also review any error codes from the CNC system related to drive communication or encoder faults.[oss-gpt-20b]