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Check all power cable connections between spindle amplifier (SPM/αi) and spindle motor for tightness, damage, or corrosion. Verify proper torque on all terminals.

LOCKOUT/TAGOUT required. Verify zero voltage with meter before touching connections.

Megger test the spindle motor windings phase-to-phase and phase-to-ground with motor disconnected. Should read >10MΩ to ground and balanced resistance between phases (typically 0.5-5Ω depending on motor size).

Disconnect motor from amplifier before megger testing to avoid damaging the drive.

Inspect motor power cables for damaged insulation, bent pins, or moisture intrusion in connectors. Check cable routing for pinch points or wear from moving machine components.

If motor winding resistance is unbalanced or insulation resistance is low, replace spindle motor. If motor tests good, replace power cable between amplifier and motor.

Check encoder cable connections at both motor and amplifier ends for tightness and pin damage. Verify cable shield is properly grounded at amplifier end only.

Do not disconnect encoder while power is on - can damage encoder circuit.

Monitor encoder signals using FANUC diagnostics (check position counter during manual spindle rotation). Verify clean A/B/Z pulse signals without dropouts. Check parameters #4020-#4025 for encoder setup.

Inspect encoder cable routing for proximity to power cables, interference sources, or mechanical damage. Maintain minimum 6-inch separation from spindle motor power cables.

If encoder signals are erratic or absent, replace encoder cable first. If problem persists, replace spindle encoder or entire motor assembly if encoder is integral.

Check spindle amplifier LED indicators for fault codes. Refer to amplifier label for LED diagnostic pattern. Check for burnt components, discoloration, or burnt smell on amplifier.

High voltage present - qualified personnel only.

Review alarm history (alarm log) for preceding alarms such as overcurrent (74), overvoltage (75), or overheating alarms that may have damaged amplifier output stage.

Disconnect motor from amplifier and megger test motor to confirm motor is not shorted. If motor tests good, perform SPM/amplifier self-diagnostics per Fanuc maintenance manual procedure.

Document all parameter settings before any amplifier replacement.

If amplifier diagnostics fail or visual damage is present, replace spindle amplifier module. After replacement, verify motor parameters (#4000 series) match motor nameplate and perform spindle parameter optimization.

Backup all parameters and PMC ladder before replacing any control modules.