What causes FANUC alarm 402?

Servo interface card is physically loose or not fully seated in the backplane slot. Servo interface card has failed or been damaged by electrical surge or heat. CNC software version is incompatible with the installed servo interface card hardware. Poor or corroded connector pins between the servo card and the main board. Card was removed or shifted during maintenance and not properly reinstalled.

How do I fix FANUC alarm 402?

1. Power down the machine completely, open the control cabinet, and locate the servo interface card. Press it firmly into its slot and check that all retaining screws or clips are secure. 2. Inspect the card and its connector for bent pins, corrosion, burn marks, or physical damage. Clean the connector with contact cleaner if needed. 3. Check the CNC system software version against the servo card part number in the Fanuc documentation to confirm they are compatible. A mismatch after a software update is a common cause. 4. Reseat all ribbon cables and connectors attached to the servo interface card, including any cables running to the servo amplifiers. 5. If the card appears undamaged and is seated correctly but the alarm persists, swap the servo interface card with a known good spare to confirm card failure before ordering a replacement. 6. Contact Fanuc support or a certified technician if the alarm remains after card replacement, as the main CPU board may also need evaluation.

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FANUC Controller

Servo/Axis · Advanced · 1-3 hours depending on parts availability

Alarm 402

Fanuc Alarm 402 - SERVO ALARM: SV CARD NOT EXIST

Alarm 402 'SV CARD NOT EXIST' indicates the CNC control cannot detect or communicate with the servo interface card (JA40/JA41 slot) or the servo software does not match the installed amplifier hardware. This commonly occurs after hardware replacement, software updates, or loose module connections in the control cabinet.

FANUCServo/AxisAdvanced1-3 hours depending on parts availability

402

Fanuc Alarm 402 - SERVO ALARM: SV CARD NOT EXIST

Servo Card Not Exist

Root Cause Summary

Alarm 402 'SV CARD NOT EXIST' indicates the CNC control cannot detect or communicate with the servo interface card (JA40/JA41 slot) or the servo software does not match the installed amplifier hardware. This commonly occurs after hardware replacement, software updates, or loose module connections in the control cabinet.

Safety

Power off before reseating card
⚠️ POWER OFF system before handling cards
Always power OFF the CNC machine and disconnect the main power supply before working on any internal components.
Be aware of potential electrical hazards when working with electrical components. Use proper grounding techniques and avoid touching exposed wires or connectors.
Wear appropriate personal protective equipment (PPE), such as safety glasses and gloves, when handling electronic components.
Discharge any static electricity before touching the servo card or other electronic components to prevent damage.
Refer to the CNC machine's documentation for specific safety instructions and warnings.

Causes and Fixes

1
Power down CNC completely. Open control cabinet and locate the servo interface card in slot JA40 (primary) or JA41 (secondary axis expansion). Verify card type matches system configuration (FSSB optical for αi/βi amplifiers, analog for older α series).
Follow lockout/tagout procedures. Discharge capacitors and wait 5 minutes after power-off before handling cards.
2
Reseat the servo interface card firmly into the slot. Check for bent pins, debris, or oxidation on card edge connectors. Inspect backplane connector for damage.
3
Power on and check LED indicators on servo interface card. Green LED should illuminate steady (FSSB systems). Check DIAGNOSIS > SERVO > FSSB STATUS screen for card detection and communication status.
4
If alarm persists, replace servo interface card with known-good spare. After replacement, verify parameter 8136 (FSSB axis configuration) matches amplifier setup. Execute SYSTEM > PMC > LADDER > MONITOR to confirm I/O handshaking.

DIY Feasiblemedium confidence

Call a technician if:

·Card hardware replacement required
·Firmware update procedures needed
·Multiple servo amplifiers showing communication errors
·Parameter corruption with no backup available

Prevention

Regular parameter backups monthly
Monitor servo interface card LED status during routine maintenance
Keep spare servo interface card with matching firmware
Document all software versions during system updates

Common Mistakes

Swapping servo cards between different software versions
Not following ESD procedures when handling cards
Changing FSSB parameters without understanding servo amplifier addressing
Powering up system before cards are fully seated

Related Alarms

401 403 404 410 411

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Always verify with your machine manual or a certified technician before performing service procedures.