16.06.2026 by Viktor Siebert
Repair of a Yaskawa SGMPH-08AAA-SE41 AC Servo Motor after Encoder Failure Caused by Coolant Ingress in a Star CNC Machine
A few weeks ago, we received a Yaskawa SGMPH-08AAA-SE41 AC Servo Motor from a Star Swiss-type lathe for inspection and repair. The motor was operating together with a Yaskawa SGDK-101010AEA-VY24 Servopack in a machine equipped with Siemens and Yaskawa control technology.
The customer reported sporadic positioning errors and unstable axis behavior. The machine was operating in an environment exposed to coolant and emulsion. Since the system was required for ongoing production, there was considerable time pressure to identify the cause quickly and implement a sustainable repair.
Initial Diagnosis
During the incoming inspection, it became apparent that the motor showed clear signs of moisture ingress.
After disassembly, the following findings were identified:
• Age-related deterioration of shaft seals
• Coolant and emulsion ingress into the motor housing
• Moisture and corrosion traces inside the encoder compartment
• Contamination of sensor elements and electrical connectors
• Early-stage oxidation of components within the feedback system
The mechanical components of the motor were still in good condition. However, the encoder had been significantly affected by the coolant contamination.
Root Cause Analysis
The technical investigation revealed the following chain of events:
• Worn shaft seals lost their protective capability
• Coolant and emulsion entered the motor housing
• The UTSIH-B13DC-E encoder became contaminated by moisture
• Position feedback signals became unstable
• The axis control system could no longer process reliable feedback data
• Initial positioning deviations and operational faults occurred
The motor itself was not the root cause of the failure. The damage was caused by progressive seal deterioration and the resulting contamination of the encoder system.
Repair Measures
Our technicians carried out the following work:
• Complete disassembly of the motor
• Removal of all coolant and emulsion residues
• Cleaning of stator, rotor and housing
• Drying of all components
• Inspection of all motor windings
• Repair and restoration of the UTSIH-B13DC-E encoder
• Replacement of all seals
• Preventive replacement of bearings
• Inspection of all connectors
• Encoder realignment and calibration
• Surface refinishing and final cleaning
After completion of the repair, the motor was reassembled and fully tested.
Final Testing and Return to Customer
The motor was tested on our test bench together with a Yaskawa SGDK-101010AEA-VY24 Servopack. Encoder feedback signals were monitored throughout the complete speed range.
The following tests were performed:
• Encoder functionality
• Positioning accuracy
• Speed performance
• Signal quality
• Temperature behavior
• Long-term stability
After successful completion of all tests, the motor was approved for return shipment.
Customer Feedback
“Thank you for the quick repair. After installation, the axis is operating reliably again and all positioning errors have disappeared.”
formation about the mentioned Servomotor and other components:
Yaskawa SGMPH-08AAA-SE41 AC Servo Motor
More information about our Yaskawa repairs can be found here.
📞 Feel free to contact us if you have any questions regarding your Yaskawa drive
Technical Specifications
| Specification | Value |
|---|
| Manufacturer | Yaskawa |
| Model | SGMPH-08AAA-SE41 |
| Motor Series | SGMPH |
| Motor Type | AC Servo Motor |
| Rated Power | 750 W |
| Rated Voltage | 200 V |
| Rated Current | 5.1 A |
| Rated Torque | 1.20 Nm |
| Rated Speed | 6000 min⁻¹ |
| Encoder | UTSIH-B13DC-E |
| Servopack | SGDK-101010AEA-VY24 |
| Machine Application | Star Swiss-Type Lathe |
| Drive Method | Direct Drive |
The values are taken directly from the motor nameplate.
Operating Conditions
| Parameter | Value |
|---|
| Ambient Temperature | 0 to +40 °C |
| Storage Temperature | -20 to +60 °C |
| Humidity | 20 to 80 %, non-condensing |
| Liquid Protection | Functional seals required |
| Mounting Method | Flange mounted |
| Application Environment | CNC machines, machine tools |
| Drive Method | Direct drive |
The general operating conditions correspond to Yaskawa M, F, S and D Series servo systems.
Integration with Other Equipment
The motor was used together with:
• Yaskawa SGDK-101010AEA-VY24 Servopack
• Siemens CNC control system
• Star Swiss-type lathe
• Yaskawa UTSIH-B13DC-E feedback system
• Yaskawa servo drive system
Functional Description
The SGMPH-08AAA-SE41 is a high-dynamic AC servo motor designed for precise positioning tasks in CNC applications.
The Servopack processes machine control commands and regulates torque, speed and position. The UTSIH-B13DC-E encoder continuously provides position feedback data required for closed-loop control.
This allows:
• High positioning accuracy
• Fast dynamic response
• Excellent control stability
• Precise axis movements
• Reliable monitoring of speed and position
The Yaskawa servo system uses continuous encoder feedback to regulate motor performance at all times.
Alarm and Error Codes
The following alarms may occur in servo systems based on the uploaded Yaskawa alarm documentation.
| Alarm | Error Name | Description | Reset | Corrective Action |
|---|
| 0x10 | Over Current | Excessive motor current | Yes | Check motor and wiring |
| 0x11 | Ground Fault | Ground leakage detected | Yes | Check insulation |
| 0x20 | Fuse Blow-Out | Internal fuse failure | Yes | Inspect power section |
| 0x40 | Over Voltage | Excessive supply voltage | Yes | Check incoming power |
| 0x41 | Low Voltage | Supply voltage too low | Yes | Check power supply |
| 0x51 | Over Speed | Excessive motor speed | Yes | Check encoder and parameters |
| 0x79 | Motor Overheat | Motor temperature too high | Yes | Check cooling and load |
| 0x81 | PG Backup Error | Encoder backup fault | Yes | Check encoder |
| 0x85 | PG Over Speed | Encoder overspeed fault | Yes | Check feedback system |
| 0xC9 | PG Communication Error | Encoder communication fault | Yes | Check encoder cable and encoder |
The alarm table is based on the uploaded Yaskawa servo alarm documentation.
Preventive Measures for the Customer
| Measure | Recommendation |
|---|
| Inspect seals | Regularly check for wear and damage |
| Monitor coolant system | Avoid direct coolant contact with motors |
| Inspect connectors | Clean during scheduled maintenance |
| Check encoder area | Monitor for moisture and corrosion |
| Monitor bearings | Check noise and running condition |
| Clean motor exterior | Remove dirt and contamination regularly |
Conclusion
This repair case demonstrates that servo motor failures are not always caused by electrical defects. In this Yaskawa SGMPH-08AAA-SE41 servo motor, aged shaft seals allowed coolant and emulsion to enter the motor housing. As a result, the UTSIH-B13DC-E encoder was damaged and reliable position feedback was no longer possible.
By repairing the encoder, replacing all seals, carrying out preventive bearing replacement and performing precise encoder calibration, the motor was successfully restored to full functionality and is now ready for many more years of reliable operation.