FANUC CNC systems may occasionally encounter complex alarms related to system memory, communication, servo feedback, or configuration errors. These issues often require deeper diagnostics and proper understanding of system architecture.
This guide covers advanced FANUC CNC alarms and troubleshooting methods to help engineers and operators quickly identify and resolve problems.
1. How to Fix FANUC ROM Parity Error (NC Basic)?
Cause
ROM parity error (NC Basic) usually indicates a FROM memory failure, which may be caused by:
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Hardware issues
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Corrupted system software
Solution
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Contact FANUC technical support
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Or consult REACO CNC technical service
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Avoid attempting unauthorized system recovery
2. How to Set Reference Point (Zero Return) in FANUC CNC?
Explanation
For semi-closed loop absolute encoder systems, reference point can theoretically be set by modifying parameters.
Method
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Set parameter:
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1815#5 = 1
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1815#4 = 1
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Important Note
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Different machine builders may define specific zero return procedures
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Always consult the machine manufacturer before performing changes
3. What Causes SV0646 Alarm?
Cause
SV0646 indicates abnormal external analog signal, typically related to:
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Linear scale (grating ruler)
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External encoder
Symptoms
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Alarm appears intermittently
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Machine may recover after restart
Troubleshooting Steps
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Check feedback cables for interference
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Ensure proper shielding and grounding
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Clean linear scale surface
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Replace:
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Linear scale
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External encoder
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SDU interface module
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4. CNC Screen Display Function Error: “CNC is being operated by another PC”
Cause
This error occurs when:
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CNC Screen Display (CSD) function is not enabled
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Another PC is already connected
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Network configuration conflict exists
Solutions
1. Check System Configuration
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Ensure CNC supports CSD function
Examples:
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0i-D → requires Ethernet function (S707)
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31i-B → requires option A02B-0207-J858
2. Check Network
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Confirm LAN connection via switch
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Ensure no other PC is connected
3. Check System Type
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Verify if CNC is open system
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Check PANEL i side configuration
5. How to Solve PS0302, DS0300, DS0306 Alarms Together?
PS0302 Solutions
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Incorrect axis movement direction → reverse direction
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Wrong zero return direction → correct movement
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Missing one-rotation signal → check encoder
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Verify parameter:
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P1005#1
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DS0300 Solution
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Reset reference point
DS0306 Solution
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Replace servo amplifier battery
6. How to Fix SV442 Alarm?
Cause
New Machine
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Missing phase in three-phase power input
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Incorrect phase sequence detected (CX48 circuit)
Existing Machine
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Power phase loss
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MCC malfunction
Solution
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Check three-phase power supply
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Verify phase sequence
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Replace:
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Power module
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Integrated servo module (if needed)
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7. What Does A2 Alarm on Power Module Mean?
Cause
A2 alarm indicates communication failure between servo modules, often accompanied by P alarm.
Solution
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Inspect fiber optic cables
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Check connections between:
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Power module
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Servo modules
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Spindle module
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Ensure all connections are secure
8. How to Fix EX1002 Alarm in FANUC 0i-MF Plus?
Cause
EX1002 is a machine builder-defined external alarm.
Solution
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Refer to machine tool manual
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Contact machine manufacturer directly
9. What Causes SV646 Alarm?
Cause
SV646 is related to:
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Linear scale
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External encoder feedback
Solution
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Inspect feedback cables
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Check encoder or scale condition
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Replace faulty components
10. How to Handle Emergency Stop Alarm?
Cause
Emergency stop alarm is triggered when:
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Emergency stop button is pressed
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Safety circuit is interrupted
Solution
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Release emergency stop button
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If alarm persists:
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Check emergency stop circuit
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Identify faulty node
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-
Contact machine manufacturer if needed
Reference Source: Beijing FANUC. This article is based on technical documentation provided by Beijing FANUC.
For More Fanuc CNC repair Cases and technical articles, please back to Fanuc Technical Support Center.
Related Articles
Here are some related technical resources you may also find helpful:
- Common FANUC CNC Alarms Classification
- FANUC Common Over Travel Alarm List
- FANUC G/ M Code for a Machining Center
- FANUC G/ M Code for lathe
- How to backup SRAM file
- How to backup All data
- How to Solve FANUC alarm 5523/5524
Technical Categories
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- Technical Guides (Backup, Parameters, Settings)
- Repair Cases & Troubleshooting Examples
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