What causes FANUC alarm 997?

ROM chip failure — age-related degradation of the ROM module. ROM module not properly seated in its socket. Electrical transient or ESD damage to the ROM chip. Firmware update interrupted or corrupted, leaving invalid ROM data. ROM socket corrosion preventing reliable read access.

How do I fix FANUC alarm 997?

1. Power cycle the machine to confirm the alarm is not transient. 2. Reseat the ROM modules in the CNC control if accessible. 3. If the alarm persists, the ROM module may need replacement — contact Fanuc for the correct part. 4. Verify the control firmware version and check with Fanuc if a re-flash is possible. 5. Contact Fanuc service — ROM parity errors typically require PCB or ROM replacement.

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FANUC Controller

System · Advanced · 60-240 minutes

Alarm 997

Fanuc 997 - ROM Parity Error (PC ROM)

Alarm 997 indicates a parity error in the PC ROM where the CNC control software resides. This is typically caused by hardware failure of the ROM chip itself, loose ROM module connections, or corruption during a firmware update. This is a critical system fault requiring immediate attention as the control cannot reliably execute software.

FANUCSystemAdvanced60-240 minutes

997

Fanuc 997 - ROM Parity Error (PC ROM)

ROM PARITY ERROR (PC ROM)

Root Cause Summary

Alarm 997 indicates a parity error in the PC ROM where the CNC control software resides. This is typically caused by hardware failure of the ROM chip itself, loose ROM module connections, or corruption during a firmware update. This is a critical system fault requiring immediate attention as the control cannot reliably execute software.

Safety

Do not operate the machine with a ROM parity error — control behavior cannot be guaranteed

Causes and Fixes

1
Power down the CNC completely and verify the main PCB board number and ROM module locations in the hardware documentation.
Always follow proper lockout/tagout procedures before opening electrical cabinets.
2
Open the control cabinet and visually inspect the ROM chip(s) on the main CPU board for physical damage, burn marks, or corrosion.
Use proper ESD protection (wrist strap and mat) when handling electronic components.
3
Reseat the ROM module(s) by carefully removing and reinstalling them to eliminate any contact issues, then power up and test.
4
If alarm persists, replace the ROM chip or entire main PCB board with a known good replacement from Fanuc or authorized supplier.
Ensure replacement ROM has correct CNC software version for your machine configuration.

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