What causes FANUC alarm 973?

Faulty or failing CNC main CPU board causing internal hardware interrupt errors. Memory module failure or corruption on the main control board. Loose or damaged ribbon cables and connectors between control boards. Power supply voltage instability or noise causing hardware faults. Failed or corrupted servo/spindle control module triggering interrupt.

How do I fix FANUC alarm 973?

1. Power the machine completely off, wait 5 minutes, then power back on to see if the alarm clears on its own. 2. Inspect all cable connections on the main CPU board and any connected modules for loose pins, corrosion, or damage. Reseat all connectors firmly. 3. Check the control cabinet power supply voltages with a multimeter. Verify 24VDC and 5VDC rails are stable and within spec under load. 4. Inspect the main CPU board and memory modules for visible damage such as burnt components, swollen capacitors, or corrosion. Replace any suspect boards. 5. If the alarm persists after reseating connections and checking power, contact Fanuc service or a qualified CNC technician as board-level replacement is likely required. 6. Document the exact conditions when the alarm occurs such as during specific operations or at random, as this helps Fanuc support narrow down the faulty hardware component.

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FANUC Controller

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

Alarm 973

Fanuc Alarm 973 - NON MASK INTERRUPT

Alarm 973 NON MASK INTERRUPT indicates a critical hardware-level fault that cannot be ignored by the CPU. This is typically caused by a defective main PCB (CPU board), memory corruption, faulty I/O module, or electrical noise/grounding issues affecting the control system. This alarm requires immediate attention as it represents a hardware failure that can cause system instability.

FANUCSystemAdvanced2-8 hours depending on parts availability

973

Fanuc Alarm 973 - NON MASK INTERRUPT

FANUC ALARM 973

Root Cause Summary

Alarm 973 NON MASK INTERRUPT indicates a critical hardware-level fault that cannot be ignored by the CPU. This is typically caused by a defective main PCB (CPU board), memory corruption, faulty I/O module, or electrical noise/grounding issues affecting the control system. This alarm requires immediate attention as it represents a hardware failure that can cause system instability.

Causes and Fixes

1
Power OFF the machine completely. Wait 30 seconds, then power ON and observe if alarm reoccurs immediately or intermittently. Document the alarm frequency pattern.
2
Access SYSTEM > MAINTENANCE > ALARM HISTORY screen and record the exact time stamps and any related alarms (especially 9XX series system alarms) that occurred before or after the 973 alarm.
3
Check diagnostic data at SYSTEM > DIAGNOSIS > check diagnostic numbers #7000-#7099 (system diagnostics) for any hardware fault indicators. Record any non-zero values.
4
If alarm persists after power cycle, replace the main CPU board (MAIN PCB). Backup all parameters and programs via CF card or network before replacement. After installation, reload parameters and ladder, then verify operation.
Ensure proper ESD precautions when handling control boards. Have replacement board configuration data ready.

Service Recommendedlow confidence

Call a technician if:

·Memory test failures
·Multiple I/O modules showing faults
·CPU diagnostic test failures
·Voltage readings outside tolerance

Prevention

Regular backup battery replacement every 2 years
Monthly temperature monitoring
Annual I/O module reseating
Quarterly power supply voltage verification

Common Mistakes

Assuming software issue when hardware diagnostics clearly indicate main board fault
Not checking backup battery voltage first
Replacing I/O modules without testing main board memory
Ignoring temperature warnings that precede NMI alarms

Related Alarms

900 999 974 975

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