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Power off the machine and check all LED indicators on the spindle amplifier faceplate. Record any lit fault LEDs and reference the amplifier hardware manual for specific fault codes.

Use proper lockout/tagout procedures before accessing electrical cabinets.

Inspect the spindle amplifier for visible damage: burnt components, swollen capacitors, tripped thermal breakers, or blown fuses on the power supply modules. Check DC bus voltage readings on the drive display if available.

Measure incoming AC power to the amplifier (all three phases) with a multimeter to verify correct voltage levels (typically 200-230V or 380-480V depending on model) and balanced phases within 2%.

Work only on de-energized circuits or use appropriate PPE and insulated tools when measuring live voltage.

If hardware faults are confirmed on the amplifier module, replace the defective spindle drive unit or contact Fanuc for module repair/exchange. Clear the alarm after replacement and verify proper operation.

Power down and inspect the spindle encoder cable from the motor to the amplifier. Check for physical damage, pinched wires, loose connectors, bent pins, or oil/coolant contamination in the connector housings.

Ensure machine is powered off and locked out before disconnecting encoder cables.

Clean encoder connectors with electronic contact cleaner and ensure proper seating. Measure cable continuity for all encoder signal wires (typically A, B, Z phase signals and +5VDC power) and check for shorts to ground or between pins.

Access spindle diagnostics on the Fanuc control (SYSTEM > PMC > DIAGN or similar path depending on control series). Verify encoder pulses are being received when manually rotating the spindle by hand in MPG mode or with M-codes disabled.

If no encoder feedback is detected after cable verification, the spindle encoder itself may be faulty. Replace the encoder assembly and perform spindle orientation calibration and parameter setup per the machine manufacturer's procedures.

Manually rotate the spindle by hand using a spindle orientation wrench or by rotating the tool holder/chuck. Check for abnormal resistance, grinding noises, or binding that indicates bearing failure or mechanical obstruction.

Remove all cutting tools and verify no workpiece is clamped before manual rotation.

Check the spindle motor thermistor circuit. Access PMC ladder or diagnostics to verify the thermistor signal is normal (not open or shorted). Measure resistance of the thermistor at the motor terminal box (should be 100-500 ohms at room temperature depending on type).

Review spindle parameters 4001-4130 (series dependent) for correct motor specifications, current limits, and thermal protection settings. Verify parameter 4055 (max current) and 4020 (motor rated current) match the motor nameplate specifications.

If mechanical binding is found, disassemble and inspect spindle bearings for contamination, wear, or insufficient lubrication. Replace damaged bearings, clean and relubricate per manufacturer specs, and verify free rotation before reassembly and testing.