Servo motor encoders are critical components in FANUC CNC systems.
If the working environment is humid, the encoder cable is damaged, or the motor experiences external impact, encoder failures may occur.
This article introduces the working principle of FANUC servo motor encoders, common alarm codes, and the correct removal and installation procedures.
1. Working Principle of FANUC Servo Motor Encoder
FANUC servo motors are equipped with a built-in pulse encoder that enables the CNC system to perform semi-closed loop position detection.
The encoder continuously transmits important feedback information to the CNC system, including:
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Position loop data
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Speed loop data
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Magnetic pole position information
At the same time, the thermistor inside the motor winding monitors internal motor temperature changes to ensure safe operation.
This real-time feedback allows the CNC system to maintain high positioning accuracy and stable servo control.
2. Common FANUC Servo Encoder Alarm Codes
When an encoder malfunction occurs, the CNC system may display the following servo alarms:
| Alarm Code | Description |
|---|---|
| SV0361 | ABNORMAL PHASE DATA (INT) – Phase data abnormality detected in the built-in pulse encoder |
| SV0364 | SOFT PHASE ALARM (INT) – Digital servo software detected an abnormal encoder phase |
| SV0365 | BROKEN LED (INT) – LED failure inside the built-in pulse encoder |
| SV0366 | PULSE MISS (INT) – Pulse error detected in the built-in encoder |
| SV0367 | COUNT MISS (INT) – Counting error detected in the encoder |
| SV0368 | SERIAL DATA ERROR (INT) – Communication data from the encoder cannot be received |
| SV0369 | DATA TRANS. ERROR (INT) – CRC error or stop-bit error during encoder data reception |
| SV0453 | SPC SOFT DISCONNECT ALARM – Software disconnection alarm of the pulse encoder |
If any of these alarms appear, the encoder or its cable may require inspection, repair, or replacement.
3. How to Identify the Encoder Model
When a servo encoder fails, first check the encoder nameplate to confirm the exact model number.
If:
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The nameplate is missing
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The label is damaged or unreadable
You can contact REACO CNC technical support, and we will assist you in identifying the correct encoder model for replacement.
4. FANUC Servo Encoder Removal and Installation
Servo motors and encoders are precision devices. During maintenance, handle them carefully to avoid contamination or mechanical damage.
Please ensure that dust and oil do not enter the encoder during the process.
Removal Procedure
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Remove the four M4 hex socket screws used to secure the encoder
(Do not loosen the M3 screws.) -
Remove the encoder and cross-shaft coupling.
Installation Procedure
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Install the new encoder, ensuring that the internal cross-shaft coupling is fully engaged.
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Tighten the encoder mounting screws.
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Screw type: Hex socket screw
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Recommended torque: 1.5 Nm
Proper installation ensures accurate feedback signals and reliable servo system performance.
FANUC Encoder Repair and Spare Parts Support
REACO CNC provides:
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FANUC CNC spare parts
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FANUC servo motors and encoders
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Mitsubishi CNC spare parts
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Professional CNC repair services
With over 33 years of industry experience, we help customers worldwide maintain and repair their CNC equipment efficiently.
If you need FANUC encoder replacement, repair services, or spare parts, feel free to contact us.
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.
