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Check amplifier LED status on the faulted axis. A solid red LED or specific blink pattern indicates amplifier hardware fault. Record the LED code pattern for reference.

Navigate to DIAGNOSIS > SERVO and check diagnostics #300-#303 (current feedback values) for the affected axis. Compare values to other axes; abnormal offset values (typically >±500) indicate amplifier circuit issues.

Power down and verify proper ventilation around the servo amplifier. Check for dust accumulation on heatsinks and cooling fans. Clean if necessary and verify ambient temperature is within specification (0-55°C).

Wait 5 minutes after power-down for DC bus capacitors to discharge before touching amplifier components.

If diagnostics confirm abnormal offset and cooling is adequate, replace the servo amplifier for the affected axis. After replacement, perform current offset auto-calibration via parameter 8162#0 (COFS) or through SYSTEM > SERVO > OFFSET menu.

Ensure motor cables are disconnected when swapping amplifiers to prevent back-EMF damage.

Power down and inspect the motor power cable connections at both amplifier (CN1) and motor ends. Check for loose connections, corrosion, bent pins, or overheating discoloration on connectors.

Verify power is off and DC bus voltage is discharged before disconnecting motor cables.

Perform insulation resistance test using megohmmeter (500VDC) between motor cable phases (U-V, V-W, U-W) and between each phase and ground/shield. Values should exceed 10MΩ. Values below 5MΩ indicate cable degradation.

Check motor cable shield continuity and verify proper grounding at amplifier end only (not at motor end). Measure DC resistance of each conductor; values should be <1Ω for typical cable lengths and balanced across all three phases.

If cable tests fail or connections show damage, replace motor power cable with Fanuc-approved cable maintaining proper routing away from AC power lines. After replacement, clear alarm and run current offset calibration from SYSTEM > SERVO > OFFSET screen.

Navigate to SYSTEM > PARAM and check parameter 8162#0 (COFS - Current Offset Detect). This should normally be set to 1. Also verify parameters 2020-2023 (servo motor parameters) match the motor model specification sheet exactly.

Check parameter 1815 (current offset value) for the affected axis. If value appears abnormal (typically should be within ±200), set parameter 8162#0=1 to force automatic recalibration on next power-up.

Perform all-parameter backup, then restore servo parameters from known good backup or reload default parameters for the specific motor model from Fanuc parameter manual. Verify motor type code in parameter 1020 matches actual installed motor.

Parameter restore will reset all servo tuning. Record custom tuning parameters before restore if modifications were made.

After parameter verification/restore, power cycle the control completely. Monitor alarm during power-on sequence. If alarm clears, perform test moves and verify normal operation. Check DIAGNOSIS > SERVO #300-#303 to confirm current offset values stabilize within normal range.