What causes FANUC alarm 971?

Machine system or function indicated by the alarm name has detected a fault. Control parameter or configuration error related to the alarm condition. Hardware component fault on the CNC or machine. Part program error or illegal operation for the indicated function. Machine interlock or safety condition not satisfied.

How do I fix FANUC alarm 971?

1. Note the alarm number and check the Fanuc alarm screen for any sub-code or additional details. 2. Identify the specific machine system or function from the alarm name. 3. Power cycle the machine to clear transient faults. 4. Consult the Fanuc parameter or operator manual for alarm 971 specific remedy. 5. Contact Fanuc service if the alarm persists after basic troubleshooting.

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FANUC Controller

System · Advanced · 2-8 hours depending on parts availability

Alarm 971

Fanuc Alarm 971 - NMI OCCURRED IN SLC

Alarm 971 NMI OCCURRED IN SLC indicates a Non-Maskable Interrupt has been detected in the Servo Logic Circuit board, pointing to a critical hardware fault. This is typically caused by memory corruption, electrical noise interference, or a failing SLC circuit board itself that requires immediate replacement.

FANUCSystemAdvanced2-8 hours depending on parts availability

971

Fanuc Alarm 971 - NMI OCCURRED IN SLC

SYSTEM ALARM 971

Root Cause Summary

Alarm 971 NMI OCCURRED IN SLC indicates a Non-Maskable Interrupt has been detected in the Servo Logic Circuit board, pointing to a critical hardware fault. This is typically caused by memory corruption, electrical noise interference, or a failing SLC circuit board itself that requires immediate replacement.

Causes and Fixes

1
Power down the system completely and perform a visual inspection of the SLC board for burnt components, bulging capacitors, or physical damage. Check for any unusual odors indicating component failure.
Disconnect all power and wait 5 minutes for capacitor discharge before handling boards.
2
Reseat the SLC board in its slot on the main CPU board or backplane. Clean the board edge connectors with contact cleaner and ensure proper seating with locking mechanisms engaged.
3
Power up and monitor alarm history via SYSTEM > ALARM > HISTORY. If alarm reoccurs immediately or within minutes, proceed to board replacement.
4
Replace the SLC board with a known good spare. After replacement, clear alarms and execute a parameter initialization sequence if required by the specific control series (consult service manual for SRAM/FROM reload procedures).
Ensure parameter and PMC program backups are current before board replacement. Battery voltage must be adequate during swap.

Service Recommendedlow confidence

Call a technician if:

·Hardware module replacement required
·Memory corruption persists after reload
·Multiple servo amplifiers showing faults
·Optical fiber testing equipment not available

Prevention

Maintain proper environmental conditions
Replace backup batteries every 5 years
Keep optical connectors clean and protected
Perform regular power supply voltage monitoring

Common Mistakes

Attempting to clear alarm without identifying root cause
Ignoring environmental factors
Not checking backup battery condition
Failing to verify parameter backup before memory operations

Related Alarms

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