Fanuc A20B‑0008‑054 is the communication interface PCB used in many FANUC CNC controllers and servo drives, handling serial I/O between the main CPU and peripheral devices. Common failure points on this class of boards include burnt or corroded surface‑mount components (especially voltage regulators and optocouplers), damaged trace connections from mechanical shock, and degraded solder joints that cause intermittent data loss. First‑check diagnostics: verify the board’s power supply rails with a multimeter (ensure 5 V/12 V lines are within spec), inspect all I/O connectors for loose or corroded pins, and review any error codes or bus‑line activity logs for patterns of communication timeout or CRC errors.[oss-gpt-20b]