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Power off the machine and lock out. Inspect all cables between the spindle motor and spindle drive unit for physical damage, oil contamination, or wear at flex points.

Verify zero voltage before handling any cables or connections.

Check all connector pins at both the spindle motor encoder/sensor connector and the amplifier side for bent pins, corrosion, or loose retention. Clean connectors with electrical contact cleaner if contamination is present.

Perform continuity test on the current sensor feedback lines using the spindle drive manual wiring diagram. Check for opens, shorts to ground, or shorts between signal pairs.

If cable damage is found, replace the spindle motor power/feedback cable assembly. Ensure proper cable routing and strain relief to prevent future failures. Verify proper shielding termination.

Check the spindle drive diagnostic LEDs and LCD display for additional fault codes or status indicators that point to internal drive faults.

Review alarm history for any preceding power-related alarms, overvoltage, or overcurrent events that may have damaged the current sensing circuits.

With power off, inspect the spindle amplifier for visible signs of component failure such as burnt resistors, damaged Hall effect sensors on the current sensing boards, or blown fuses specific to the sensor circuits.

Only qualified personnel should open drive units due to high voltage hazards.

If internal drive fault is confirmed, replace the current sensing board or the entire spindle drive module per Fanuc service procedures. Test with known good drive unit if available for verification.

Check spindle motor operating history for overheating incidents, bearing noise, or contamination that may have damaged internal sensors. Review maintenance logs and thermal overload alarms.

Measure the resistance of the current sensor windings or Hall sensor power supply circuits at the motor connection point per motor specifications. Compare readings to acceptable ranges in the motor manual.

If accessible, inspect the motor feedback connector area for moisture, coolant contamination, or damaged seals that may have compromised the sensor electronics.

If motor internal sensor failure is confirmed, the spindle motor requires replacement or rebuild with new sensor assembly. Coordinate with Fanuc or authorized motor repair facility for sensor module replacement.