400

Navigate to DIAGNOSIS > SERVO and check diagnostic screen #201 (servo alarm detail) to identify the specific axis number and alarm sub-code. Record the displayed values for torque and current.

Check diagnostics #720 and #721 (servo load meter) for the affected axis. Values consistently above 80-85% indicate excessive mechanical load. Compare current readings against historical baseline values.

Manually rotate the motor shaft with the servo OFF (parameter P2000#0 SVO=0 or use emergency stop). Check for grinding, tight spots, bearing seizure, or collision with crash debris. Inspect ballscrew/coupling for damage.

Disable high voltage before manual inspection. Use EMERGENCY STOP or disconnect amplifier power.

Inspect way lubrication system and verify adequate oil flow. Check ballscrew nut preload and guide wear. Remove covers and verify no chips, coolant sludge, or foreign objects are obstructing travel.

Verify motor code parameter P1020 (axis motor serial number) matches the physical motor label. Cross-reference with Fanuc motor specification manual to confirm parameters P1825 (motor rated current), P1826 (motor maximum current), and P1828 (motor torque constant).

Check acceleration parameters P1620 (rapid traverse acceleration time constant) and P1622 (cutting feed acceleration time constant). Values too low (<50ms) demand high torque rates. Increase incrementally by 20-30ms and retest.

Review servo gain parameters: P2020-P2023 (position loop gain), P2030-P2033 (velocity loop gain), P2040-P2041 (integration time constants). If recently changed or after battery replacement, restore from backup or use Fanuc default tuning data for the motor model.

Incorrect gains can cause oscillation or runaway. Change one axis at a time and test in JOG mode at low feedrates first.

Check parameter P2024 (load inertia ratio). If incorrectly set too high, the amplifier may apply excessive current compensation. Typical ratios are 1-30. Recalculate based on machine mechanics or use servo tuning function (SYSTEM > SERVO > TUNING).

Check amplifier LED status codes on the αi or βi servo amplifier front panel. Steady red or flashing patterns indicate internal faults. Cross-reference LED code with amplifier manual. Check diagnostic #395 (amplifier alarm history) for recurring faults.

Monitor diagnostic #300-#307 (servo motor load current) during light air-cut motion. Compare amperage between axes. If the affected axis draws 30-50% more current for identical moves, motor efficiency has degraded. Listen for unusual bearing noise or vibration.

Check motor cooling fan operation and amplifier heat sink temperature. Verify ambient temperature <40°C and cabinet ventilation. Overheating reduces amplifier current capacity. Check diagnostic #028 (amplifier regeneration load) for excessive values indicating brake resistor issues.

Test motor insulation resistance with megohmmeter (amplifier disconnected). Minimum 10MΩ at 500VDC. Values <5MΩ indicate winding contamination or insulation breakdown. Inspect motor cable for damage, verify shield grounding, and check connector pins for corrosion.

Disconnect all motor power cables before insulation testing. High voltage test equipment can damage amplifier if connected.