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Power off the machine and manually rotate the spindle by hand using a strap wrench on the taper or pulley. Check for rough spots, grinding sounds, or complete seizure.

Ensure drive power is OFF before manual rotation to prevent back-EMF damage to the amplifier.

Remove any tool holder and drawbar assembly. Inspect for debris, coolant contamination in bearings, or damaged drawbar mechanisms that may cause binding.

Tag out machine power during mechanical inspection.

Check spindle bearing condition by measuring radial and axial play. Excessive play or heat discoloration on the spindle nose indicates bearing failure requiring replacement.

Inspect for crash damage to spindle shaft, bent tooling, or housing distortion that may cause rotor-to-stator contact. Measure spindle runout with dial indicator (should be <0.0002" TIR).

Perform megohm insulation test on spindle motor windings (U, V, W to ground) with drive disconnected. Reading below 5 megohms indicates insulation failure requiring motor replacement or rebuild.

Disconnect motor power cables at amplifier before testing. Discharge motor capacitance before handling.

Inspect motor power cables for damage, coolant contamination, pinch points, or worn insulation. Check cable routing through cable tracks for abraded sections contacting metal surfaces.

Check spindle motor encoder feedback cable for damage or contamination. A failing encoder can cause commutation errors leading to current spikes during rotation.

If motor tests fail, disconnect motor from drive completely and run drive diagnostics (check parameters 3705-3707 for amplifier self-test). This isolates whether fault is motor-side or drive-side.

Do not run amplifier without proper load or manufacturer-approved no-load testing procedure.

Verify spindle motor parameters match motor nameplate: check parameter 3735 (max current), 3736 (rated current), 3740 (motor poles), and 3741 (motor constants). Incorrect values prevent proper current control.

Check alarm history and drive LEDs on spindle amplifier module. Multiple rapid overcurrent alarms indicate amplifier component failure. Record LED status codes for module diagnostics.

Measure DC bus voltage at amplifier (typically 280-320VDC for 200V class). Low bus voltage causes compensatory current increase. Check regenerative discharge resistors and power supply module.

High voltage present. Use insulated test equipment rated for 600V+. Qualified personnel only.

If mechanical and motor tests pass, suspect failed IPM (Intelligent Power Module) or transistor block in amplifier. This requires amplifier module replacement or repair by qualified Fanuc service personnel.

Amplifier modules contain high-energy capacitors. Allow 5+ minutes discharge time after power removal before handling.