403

Power down the CNC and check the servo amplifier LED display on the faulted axis. Record the LED pattern (typically 7-segment display showing alphanumeric codes). Refer to the amplifier hardware manual for LED code interpretation (common codes: 9, A, 25, 40 indicate hardware faults).

Ensure LOTO procedures before opening cabinet doors or inspecting amplifier modules.

Access DIAGNOSIS screen > SERVO > Check diagnostics #300-#399 series for detailed servo alarm information. Record diagnostic #397 (servo alarm detail) and #400-#407 (amplifier status) for the faulted axis.

Inspect the amplifier module for visible damage: burnt components, capacitor bulging, or discoloration. Check all connector cables between amplifier and motor (power and feedback cables) for damage or loose connections.

If amplifier shows hardware fault LED code and no external issues found, replace the servo amplifier module. After replacement, perform axis reference point return and verify operation. Check parameter 1815#0 (absolute position establishment) if using absolute encoders.

Replacing amplifier on absolute encoder systems requires position re-establishment procedure per Fanuc manual.

Check the DC link voltage at the servo amplifier. Verify main circuit DC bus voltage is within specification (typically 280-310VDC for 200V class, 530-660VDC for 400V class). Measure voltage at amplifier input terminals with a qualified multimeter.

High voltage present. Use appropriate PPE and follow electrical safety procedures.

Inspect fuses on the servo amplifier module. Check both main circuit fuses and control circuit fuses (typically located on amplifier front panel or in PSM power supply module). Replace any blown fuses and investigate cause before re-energizing.

Verify +24VDC control voltage supply to the amplifier. Measure at CX1A/CX1B connectors on amplifier. Voltage should be stable 24VDC ±10%. Check diagnostic #398 (control power voltage) if available on your control series.

Check the Power Supply Module (PSM) LED indicators. If PSM shows fault condition, measure input AC voltage (200VAC or 400VAC 3-phase) and inspect regenerative discharge resistor connections and resistance values per amplifier specifications.

Access DIAGNOSIS screen > SERVO > Check diagnostics #300 (serial pulse coder alarm). For serial encoders (αi series), check diagnostic #314 (encoder communication error details). Record any non-zero values indicating encoder fault codes.

Power down and inspect encoder cable from motor to amplifier. Check for cable damage, excessive bending near connectors, contamination, or loose connections at both motor and amplifier ends. Verify cable shield grounding is intact. Measure cable continuity if damage suspected.

Check parameter 1815 (encoder type), 1825 (serial encoder setting), and 1827 (encoder data settings) match the actual encoder installed on the motor. Mismatch can cause communication failures interpreted as hardware errors.

If encoder cable and parameters verified correct, the encoder itself may be faulty. Replace encoder or motor assembly. After replacement, perform encoder battery backup reset (parameter 1815#1) if applicable, and execute reference position return. Verify operation under load conditions.

Encoder replacement requires careful alignment and may require Fanuc authorized service for sealed motors.