Common Causes of Alarm 2 or Alarm 31
- Spindle drive malfunction
- Spindle motor feedback signal failure
- Mechanical obstruction or defect
- Faulty wiring between the drive and the motor
- Damaged contactor on motor lead lines between the motor and drive
- Faulty or misaligned sensor
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How to Check If the FANUC Drive Is Functioning Properly
- Issue an M-code command for zero spindle speed and observe whether an alarm is triggered.
- Check whether the drive is actively locking the spindle. (If the spindle is not locked, this typically indicates a drive fault.)
Alarm 2 or 31 Repair Procedure for Belt-Driven Spindles
These alarms are often associated with speed deviation errors caused by improper sensor-to-gear gap when reinstalling a spindle motor on machines with a belt-driven spindle. Incorrect belt tension can push the sensor gear too close or too far from the sensor, triggering the fault.
Step-by-Step Sensor Adjustment:
- Disconnect the fan wire located inside the terminal box.
- Remove the four bolts securing the fan and fan cover to the motor.
- Remove the four screws attaching the sensor cover to the motor.
- Loosen the two screws securing the sensor in place. Insert a piece of standard copy paper or a piece of cigarette cellophane between the sensor and the gear. Adjust the sensor position to create a precise gap that allows the paper to slide out with light resistance. (Use the paper or film to gently press the sensor against the gear to achieve the correct spacing.)
- Tighten the two sensor screws and slowly rotate the motor shaft to ensure there is no contact between the gear and the sensor.
- Reassemble all bolts and screws in reverse order.
If issues persist after completing the steps above, further inspection of the drive module, feedback circuitry, or replacement of damaged components may be necessary. For genuine Fanuc spare motors, professional diagnostics, or repair support, contact CIT Automation Equipment—your trusted supplier for industrial automation solutions.
