What causes FANUC alarm 772?

Spindle amplifier internal fault — check drive for displayed fault code. Spindle encoder cable or connector fault. Spindle motor overload from heavy cutting conditions. Spindle motor cooling fan failure. Spindle drive parameter configuration error.

How do I fix FANUC alarm 772?

1. Check the spindle amplifier fault LED and displayed fault code. 2. Review Fanuc spindle alarm details for the specific SP sub-code. 3. Check spindle encoder cable and connectors. 4. Reduce cutting load and verify if alarm clears. 5. Power cycle after addressing identified faults.

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FANUC Controller

Spindle · Intermediate · 30-60 minutes

Alarm 772

Fanuc Alarm 772 - SPINDLE-3 MODE CHANGE ERROR

Fanuc Alarm 772 SPINDLE-3 MODE CHANGE ERROR occurs when the CNC cannot execute a mode change command (orientation, C-axis, spindle mode) for the third spindle. This is typically caused by parameter configuration errors, serial spindle communication problems, or spindle amplifier feedback issues preventing proper mode transition acknowledgment.

FANUCSpindleIntermediate30-60 minutes

772

Fanuc Alarm 772 - SPINDLE-3 MODE CHANGE ERROR

SYSTEM ALARM 772

Root Cause Summary

Fanuc Alarm 772 SPINDLE-3 MODE CHANGE ERROR occurs when the CNC cannot execute a mode change command (orientation, C-axis, spindle mode) for the third spindle. This is typically caused by parameter configuration errors, serial spindle communication problems, or spindle amplifier feedback issues preventing proper mode transition acknowledgment.

Causes and Fixes

1
Navigate to SYSTEM > PARAM and verify parameter 4001#0 (serial spindle enable) is set to 1. Check parameter 4020 to confirm spindle-3 axis number assignment (typically set to 5 for third spindle).
2
Check parameter 4130 (spindle mode change waiting time) and increase if set below 500ms. Verify parameter 4131 (spindle mode change completion signal mask time) is properly configured, typically 50-200ms.
3
Navigate to SYSTEM > DIAGNOSIS and check diagnostic 441 (spindle serial communication status). Bit 0 should show serial communication active. Check diagnostic 445-447 for spindle-3 specific communication errors.
4
Verify parameter 3742 (spindle C-axis selection) bit settings for spindle-3. Check parameter 4002 (spindle motor type) matches the actual spindle motor configuration for SP3.
Parameter changes require power cycle. Record original values before modification.

DIY Feasiblehigh confidence

Call a technician if:

·Spindle amplifier hardware failure
·Mechanical gear change mechanism requires disassembly
·Serial communication hardware issues

Prevention

Regular spindle parameter backup
Periodic gear change mechanism lubrication
Monitor spindle load trends
Maintain proper pneumatic/hydraulic pressure

Common Mistakes

Changing mode parameters without understanding spindle hardware
Ignoring load conditions during mode changes
Not verifying gear position feedback before parameter changes
Attempting mode changes while spindle is under load

Related Alarms

770 771 773 410 411

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