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Power off the machine and lock out electrical supply per safety procedures.

High voltage present in spindle motor area - follow LOTO protocols

Locate the acoustic sensor cable running from the spindle motor housing to the spindle amplifier (typically a shielded 2-4 conductor cable with M8 or M12 connector at sensor).

Inspect cable for physical damage, coolant contamination, burned insulation, or loose connections. Check connector pins for corrosion or bent contacts. Verify cable routing is not pinched or rubbing against sharp edges.

Disconnect cable at both ends and measure continuity between each conductor and verify >10M ohm resistance to ground/shield. Replace cable if any conductor shows open circuit or <1M ohm to ground.

Access the spindle motor rear cover or sensor mounting location (typically on motor housing near rear bearing). Note sensor model number and mounting location for reference.

Allow spindle to cool below 40°C before accessing sensor area

Check sensor mounting torque per spindle manual specifications (typically 5-8 N·m for M8 sensors). Verify sensor face makes full contact with mounting surface and no coolant/oil contamination is present on mating surfaces.

Disconnect sensor and measure DC resistance across sensor leads - should read between 100-500 ohms for most piezo sensors. If open circuit or short circuit detected, sensor has failed internally.

If measurements are normal, clean mounting surface with brake cleaner, apply light coating of thermal paste if specified, reinstall sensor to proper torque, and test. If alarm persists, replace sensor with OEM equivalent part.

Access spindle amplifier diagnostics through the FANUC maintenance screen: SYSTEM > MAINTENANCE > SP SENSOR or SP AMP diagnostics. Record all displayed voltage and status values.

Check amplifier acoustic sensor power supply voltage (typically +24VDC or ±15VDC depending on sensor type). Navigate to SP parameter screen and verify sensor enable parameters are set correctly per machine builder specifications.

Perform amplifier self-test if available through diagnostics menu. Check for additional fault codes or LED indicators on the spindle amplifier module that may indicate specific circuit board failures.

If power supply voltages are incorrect or self-test fails, power down and inspect amplifier acoustic sensor PCB for burnt components, swollen capacitors, or corrosion. Replace spindle amplifier acoustic sensor board or entire amplifier module if hardware fault confirmed.

Spindle amplifier replacement requires motor parameters backup and restoration - document all settings before replacement