15.05.2026 by Viktor Siebert
Production Downtime Caused by Yaskawa SGMPH-08A1A-SE31 Servo Motor with Encoder Failure on UTSAH-B16DC-E
A defective servo drive system in an industrial production machine caused recurring communication errors between a Yaskawa SGMPH-08A1A-SE31 servo motor and the connected SGDK-101010AEA-V servopack. The machine experienced multiple unplanned stoppages, creating production interruptions and significant time pressure within the manufacturing process.
Initially, the customer suspected a cable fault and replaced the complete motor cable assembly. However, the communication fault remained unchanged. Only a detailed diagnostic analysis on the test bench revealed the actual root cause inside the motor encoder system.
The repair was completed in our servo laboratory including a full preventive motor overhaul.
Introduction to the Service Case
The affected machine operated in a highly automated production environment with demanding cycle times. Even short interruptions resulted in production losses and scheduling problems.
After several sporadic shutdowns, the servo amplifier continuously reported a communication error. At first, a defective cable between the motor and servopack was suspected. The customer therefore replaced the entire encoder and power cable assembly without success.
Since the problem persisted, the Yaskawa SGMPH-08A1A-SE31 servo motor was sent to our facility for detailed diagnostics.
During the incoming inspection it became immediately clear that no stable encoder communication could be established between the UTSAH-B16DC-E encoder and the Yaskawa servopack.
Initial Diagnosis
The visual inspection showed no major mechanical damage on the motor housing or connector system.
The following tests were performed:
- insulation measurement of motor windings
- phase resistance measurement
- encoder supply voltage analysis
- feedback signal diagnostics
- connector inspection
- servopack load testing
The motor was tested using a Yaskawa SGDK servopack.
During testing the following abnormalities were detected:
- unstable encoder communication
- missing feedback signals
- intermittent signal interruptions
- unsuccessful encoder initialization
The observed symptoms matched typical Yaskawa encoder and communication faults documented in the service manuals. Typical alarm patterns include PG Communication Error, Wire Break and Encoder Signal Error.
Additional Yaskawa-related faults considered during diagnosis included:
| Drive Code | Description |
|---|
| 0xC9 | PG communication error |
| 0xC3 | Wire break in pulse encoder |
| 0x65 | INC signal error |
| 0x82 | PG sum check error |
| 0x83 | PG battery error |
Root Cause Analysis
After disassembling the UTSAH-B16DC-E encoder, the actual defect could be identified.
The failure was caused by an electronic defect inside the encoder system.
The following issues were detected:
- damaged signal conditioning electronics
- unstable feedback signals
- thermally stressed electronic components
- internal contact issues inside the sensor assembly
- age-related electronic degradation
The defect caused:
- loss of communication with the servopack
- incorrect position feedback
- servo initialization faults
- complete machine downtime
Repairing the encoder required extremely precise micro-electronic and mechanical work. Such repairs are comparable to watchmaking and require specialized procedures, tools and extensive experience.
Repair Measures
The following work was completed during the repair process:
- complete motor disassembly
- encoder disassembly
- repair of encoder electronics
- signal path restoration
- replacement of worn bearings
- replacement of all seals
- complete cleaning process
- resealing of the motor
- repainting of the housing
- connector inspection
- winding insulation testing
- vibration analysis
- thermal testing
The encoder was tested multiple times under real operating conditions.
In addition, the complete motor received a preventive overhaul to minimize the risk of future failures.
Final Testing and Shipment
After completing the repair, the motor underwent extensive testing:
- industrial servo motor test bench operation
- testing with original Yaskawa servopack
- load testing
- speed testing
- temperature monitoring
- encoder signal verification
- communication stability analysis
The motor was also tested on an original production machine.
The communication fault no longer occurred. Encoder feedback operated reliably and without interruption.
After successful long-term testing, the motor was prepared for return shipment.
Customer Feedback
“After the repair the machine immediately returned to stable operation. We were especially impressed that the encoder itself could be repaired after previous unsuccessful cable replacement attempts.”
Information about the mentioned Servomotor and other components:
Yaskawa AC Servo Motors SGMPH-08A1A-SE31
More information about our Yaskawa repairs can be found here.
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Technical Specifications
| Specification | Value |
|---|
| Manufacturer | Yaskawa |
| Model | SGMPH-08A1A-SE31 |
| Device Type | AC Servo Motor |
| Power Output | 750 W |
| Voltage | 200 V |
| Current | 4.1 A |
| Torque | 2.39 Nm |
| Rated Speed | 3000 r/min |
| Insulation Class | Class B |
| Encoder | UTSAH-B16DC-E |
| Associated Servopack | SGDK-101010AEA-V |
| Cooling | Self-cooled |
| Motor Type | Permanent Magnet Servo Motor |
General Yaskawa servo motor specifications are based on the M/F/S/D series documentation.
Operating Conditions
| Parameter | Range |
|---|
| Ambient Temperature | 0 to +40 °C |
| Storage Temperature | -20 to +60 °C |
| Humidity | 20 to 80 % |
| Mounting Type | Flange mounted |
| Cooling | Self-cooled |
| Environment | Industrial environment |
| Oil/Water Protection | Required |
| Vibration Limit | According to Yaskawa specifications |
Integration with Other Equipment
The SGMPH-08A1A-SE31 servo motor operates together with:
- Yaskawa SGDK servopacks
- Yaskawa SERVOPACK CACR-SR
- CNC controllers
- machine tools
- positioning systems
- industrial automation systems
- encoder feedback systems
- motion control and fieldbus systems
Motor and servopack combinations are documented in the Yaskawa compatibility tables.
Functional Description
The Yaskawa SGMPH-08A1A-SE31 is a permanent magnet AC servo motor designed for precise positioning and speed control applications.
The system operates using:
- encoder feedback
- closed-loop control
- PWM-controlled power stage
- high-resolution position feedback
- overcurrent protection
- overvoltage protection
- overload protection
- temperature monitoring
Encoder feedback is essential for:
- speed control
- positioning accuracy
- synchronization
- CNC axis control
Even minor disturbances in encoder communication can immediately generate alarms or complete machine shutdowns.
Alarm and Error Codes
| Alarm | Error Name | Meaning | Reset | Action |
|---|
| 0xC9 | PG communication error | Encoder communication failure | Power reset | Check encoder |
| 0xC3 | Wire break encoder | Encoder signal interruption | Reset possible | Check cable/encoder |
| 0x65 | INC signal error | Incremental encoder error | Reset | Check encoder |
| 0x82 | PG sum check error | Encoder checksum error | Reset | Repair/replace encoder |
| 0x83 | PG battery error | Battery error | Reset | Check battery |
| 0x84 | PG overspeed | Encoder overspeed error | Reset | Check mechanics |
| 0x85 | PG overheat | Encoder overheating | Reset | Check cooling |
| 0x81 | PG backup error | Backup failure | Reset | Check encoder |
| 0xE6 | Network communication error | Communication fault | Reset | Check communication |
| 0xE7 | Link setting error | Link configuration fault | Reset | Verify parameters |
Main Components
| Component | Function |
|---|
| Stator | Motor drive section |
| Rotor | Torque transmission |
| Encoder UTSAH-B16DC-E | Position feedback |
| Bearings | Mechanical guidance |
| Seals | Protection against contamination |
| Connectors | Signal and power transmission |
| SGDK Servopack | Power regulation |
| Power section | Motor current supply |
| Feedback electronics | Encoder signal processing |
Preventive Recommendations
To reduce the risk of future failures we recommend:
- regular connector inspections
- thermal monitoring of servo motors
- encoder cable inspections
- bearing replacement when abnormal noise occurs
- cleaning of cooling surfaces
- inspection of cable shielding
- preventive seal replacement
- regular insulation testing
- vibration analysis
- documented maintenance intervals
Encoder-related failures often develop gradually and initially appear only as intermittent communication faults.
Conclusion
The defect inside the UTSAH-B16DC-E encoder caused a complete communication failure between the servo motor and servopack. Only detailed laboratory diagnostics revealed the actual root cause.
By repairing the encoder electronics and performing a preventive motor overhaul, the servo motor could be fully restored to operational condition.
Regular maintenance and early diagnostics help prevent unplanned production downtime and significantly reduce long-term maintenance costs.
Technical references are based on the provided Yaskawa manuals and alarm documentation.