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Check the 7-segment LED display on the faulted axis servo amplifier module (Alpha-i or Beta-i series). Record the alarm code displayed (e.g., A.10, A.20, A.61, etc.). Refer to the amplifier manual for specific sub-alarm definitions.

Navigate to DIAGNOSIS > SERVO screen and check diagnostic numbers D0300-D0307 (servo alarm history) and D0320-D0327 (amplifier status) for the affected axis to identify detailed fault conditions.

Check DC bus voltage at DIAGNOSIS > SERVO, diagnostic D0020 (DC link voltage). Normal range is 280-330VDC for 200V class, 530-680VDC for 400V class. Out-of-range values indicate power supply or regenerative discharge issues.

If amplifier shows overload alarm (A.10/A.20 series), inspect motor cables for shorts, check motor insulation resistance (should be >10MΩ at 500VDC test), and verify parameter 2020 (motor type code) matches the actual motor model installed.

Disconnect motor cables before performing insulation tests to avoid damaging amplifier circuits

Verify 24VDC control power at amplifier terminal DCIN/COM. Check for stable voltage between 20-28VDC. Inspect PSU-B (power supply unit) LED indicators for control voltage status.

Inspect optical fiber cables between CNC (JD1A/JD1B connectors) and servo amplifier (JL1A/JL1B). Clean fiber ends with approved solvent and lint-free cloth if dusty. Replace fiber cables if physical damage is visible.

Check JA7/JA8 connector seating on the amplifier serial interface. Reseat connectors firmly. On older Alpha-i systems, verify ribbon cable integrity between CNC and amplifier rack.

Power down CNC completely before reseating any amplifier interface connectors

Check parameter 8131 bit 1 (serial pulse coder selection) matches the encoder type. Verify parameter 1815 (amplifier type) and 1020 (servo axis serial number) are correctly configured for the installed amplifier.

Check regenerative discharge resistor unit (typically mounted separately or on amplifier). Measure resistance between terminals: should read specified value (commonly 40-100Ω for 200V, 200-300Ω for 400V class). Open circuit indicates failed resistor.

Allow 15 minutes after power-down for DC bus capacitors to discharge before measuring resistor

Navigate to DIAGNOSIS > SERVO and monitor D0020 (DC bus voltage) during axis motion. Voltage spikes above 390VDC (200V class) or 780VDC (400V class) during deceleration indicate inadequate regenerative handling.

Check parameter 1825 (rapid traverse rate) and 1826 (acceleration time constant). Reduce acceleration/deceleration rates temporarily by increasing parameter 1826 to test if regenerative overload is occurring on rapid moves.

Inspect amplifier LED for A.61 (overvoltage) alarm. If present and regenerative resistor is good, check regenerative transistor and control circuit on amplifier PCB. Replacement of power supply module or amplifier may be required.