404

Power down the system completely. Inspect all interface cables between the CNC control unit and the affected axis servo amplifier. For FSSB systems, check JD1A/JD1B optical fiber connections for damage, contamination, or loose connections. For analog/serial systems, verify CNxx connector integrity.

Ensure proper lockout/tagout procedures before working on connections. Do not disconnect cables while power is applied.

Navigate to SYSTEM > DIAGNOSIS > SERVO screen and check diagnostic number 200 (axis control status) and diagnostic 300-307 (FSSB communication status). Verify communication is established for the affected axis number indicated in the alarm.

Check the servo amplifier LED display. A normal READY state shows green LED solid. Red or flashing LEDs indicate amplifier faults. Cross-reference LED codes with amplifier model documentation (αi series: AL### codes, βi series: A### codes).

Verify parameter 1020 (serial interface type: 0=separate, 1=serial, 4=FSSB) matches your hardware configuration. Incorrect settings prevent proper MCON/DRDY handshaking.

Check servo amplifier power supply voltages. Navigate to SYSTEM > DIAGNOSIS > SERVO and verify diagnostic 380 (DC link voltage) shows nominal value (typically 280-320VDC for 200V class, 530-670VDC for 400V class). Low or fluctuating DC bus voltage indicates power supply problems.

Inspect the servo amplifier control power circuit. Verify 24VDC control power supply (CNMT or CNMC connector) is present and stable. Measure voltage at amplifier terminals to confirm 24VDC ±10%.

Perform amplifier reset by powering down the complete system for 60 seconds, then power up and observe startup sequence. If 404 alarm appears immediately on power-up before any motion commands, the amplifier is likely faulty.

If available, swap the suspected amplifier with a known-good identical unit or swap axis positions in parameter 1020#0-1023 (axis-to-amplifier assignment) to isolate whether fault follows the amplifier or remains with the axis position.

Only qualified personnel should swap amplifiers. Verify all parameter settings and motor specifications match before testing.

Navigate to SYSTEM > DIAGNOSIS > PARAMETER and check diagnostic 001 (software version) and diagnostic 000 (system configuration). Verify the correct axis control card/module is recognized. Missing or incorrect module detection indicates hardware failure.

Check parameter 1020 (servo interface type) and parameter 1023 (axis control assignment). Verify settings match the installed hardware. Incorrect axis assignment can cause MCON/DRDY mismatch on specific axes.

Inspect the CNC control unit internal connections for the servo interface board (JD1 optical fiber board for FSSB or serial servo interface card). Reseat the module in its slot and verify secure connection to the main CPU board.

Power down and follow ESD precautions when handling internal CNC PCBs. Use proper grounding straps.

Contact Fanuc service with the complete alarm history (SYSTEM > ALARM > HISTORY) and system configuration data. Hardware-level CNC failures require factory diagnostics and may need board replacement with subsequent parameter reload from backup.