ROM Parity Error
Fanuc · Series 20 CNC
What does 900 mean?
This alarm indicates a parity error has been detected in the Read-Only Memory (ROM) of the Fanuc Series 20 CNC. This means that data stored in the ROM, which contains the CNC's operating system and critical programs, has become corrupted or cannot be read reliably, making the control system unstable or inoperable.
Common Causes
- Faulty ROM chip(s) on the CNC main board.
- Transient power fluctuation or electrical noise affecting memory integrity.
- Physical damage to the CNC main board.
- Aging or defective memory components.
Repair Steps & Checklist
Click steps to track your progress.
- 1
Power cycle the CNC system completely (turn off and then on) to see if the error is a transient issue.
- 2
Verify stable and clean power supply to the CNC main unit, checking for voltage sags or spikes.
- 3
Inspect the CNC main board for any visible damage, loose chips, or corrosion.
- 4
If the alarm persists, it often indicates a faulty CNC main board or ROM module that requires replacement.
- 5
Consult Fanuc service documentation for specific diagnostic procedures for memory errors.