10.06.2026 by Viktor Siebert
Repair of a Yaskawa SGMGH-30DCA6H-OY Servo Motor: Axis Dropping Due to Defective Holding Brake
Introduction: A Real Service Case
A customer from the machine tool industry contacted us because an axis could no longer hold its position safely when stopped. The axis repeatedly dropped downward although the drive system had been switched off correctly. The machine could still operate in a limited manner, however there was a significant risk to the workpiece, tooling and machine.
For analysis, the Yaskawa AC Servo Motor SGMGH-30DCA6H-OY together with the installed UTSIH-B17CK encoder was sent to our workshop. The motor operates in combination with a Yaskawa SGDH-30DE Servopack and is equipped with an electromagnetic holding brake type Ogura RNB 4.4G-03 A.
The fault description already indicated a brake system problem. The subsequent inspection confirmed this suspicion.
Initial Diagnosis
The incoming inspection immediately revealed several abnormalities:
• The axis could not be held safely when power was removed
• Significant contamination around the brake assembly
• Brake dust inside the motor
• Bearing noise when rotating the shaft
• Contamination in the encoder area
Disassembly showed that the brake was mechanically worn. Fine brake dust generated over time had spread throughout the motor.
The most affected components were:
• Holding brake
• Encoder section
• Ball bearings
• Seals
Actual Root Cause
The technical analysis revealed the following chain of failure:
• Wear of the Ogura holding brake
• Generation of brake dust over an extended period
• Distribution of brake dust inside the motor
• Contamination of the encoder area
• Damage to the ball bearings caused by abrasive particles
• Increased friction and growing bearing noise
• Loss of reliable holding function of the axis
The original fault was therefore clearly located in the mechanical brake assembly. Secondary damage affected both the encoder and the bearings.
Repair Measures
The motor was completely disassembled and rebuilt.
The following work was carried out:
• Removal of the defective Ogura RNB 4.4G-03 A brake
• Installation of a new holding brake
• Removal and inspection of the UTSIH-B17CK encoder
• Cleaning of brake dust contamination from the encoder
• Replacement of motor bearings
• Cleaning of all assemblies
• Inspection of winding insulation
• Replacement of seals
• Reassembly and adjustment of all components
• Functional testing under load
Special attention was given to the complete removal of brake dust, as even small residues can cause long term damage.
Final Testing and Return Shipment
After completion of the repair, the motor was tested on our test bench together with a Yaskawa SGDH-30DE Servopack.
The following parameters were verified:
• Speed performance
• Encoder feedback
• Brake operation
• Temperature behavior
• Bearing noise
• Smooth running
• Insulation values
All measured values were within specification. The holding brake operated correctly again and the axis could be safely held in position.
The motor was then prepared for return shipment.
Customer Feedback
“The axis now reliably holds its position again after reinstallation. The previous dropping issue has completely disappeared.”
Information about the mentioned Servopack and Servomotor:
More information about our Yaskawa repairs can be found here.
📞 Feel free to contact us if you have any questions regarding your Yaskawa drive technology. Our experienced team is always ready to assist you.
Technical Specifications
| Parameter | Value |
|---|
| Manufacturer | Yaskawa Electric |
| Model | SGMGH-30DCA6H-OY |
| Motor Type | AC Servo Motor |
| Rated Output | 2900 W |
| Rated Torque | 18.6 Nm |
| Rated Speed | 1500 min⁻¹ |
| Rated Current | 11.9 A |
| Rated Voltage | 400 V |
| Insulation Class | F |
| Encoder | UTSIH-B17CK |
| Brake | Ogura RNB 4.4G-03 A |
| Servopack | SGDH-30DE |
| Country of Origin | Made in Japan |
The performance data was taken directly from the motor nameplate. The motor belongs to the Sigma II series and is operated together with the SGDH-30DE Servopack.
Operating Conditions
| Parameter | Value |
|---|
| Ambient Temperature | 0 to +40 °C |
| Storage Temperature | -20 to +60 °C |
| Humidity | 20 to 80 % non-condensing |
| Mounting | Flange mounted |
| Protection Class | IP65 excluding shaft outlet |
| Cooling | Totally enclosed, self-cooled |
| Excitation | Permanent magnet |
The environmental specifications correspond to the Yaskawa servo motor series data.
Operation with Other Equipment
The motor is typically operated together with:
| Device | Function |
|---|
| Yaskawa SGDH-30DE | Servo Amplifier |
| Yaskawa SGDH Sigma II Series | Motion Control |
| CNC Controllers | Positioning |
| Machine Tools | Feed Axes |
| Machining Centers | Axis Drives |
| Automation Systems | Precision Motion |
Functional Description
The SGMGH-30DCA6H-OY is an AC servo motor from the Yaskawa Sigma II series. Speed and position control are performed through the UTSIH-B17CK encoder. The feedback system enables highly precise positioning even during dynamic motion sequences.
The integrated holding brake is intended exclusively for safely holding the axis when stationary. It is not a service brake. Its purpose is to prevent vertical axes from dropping when the servo amplifier is switched off.
The connected SGDH-30DE Servopack performs:
• Current control
• Torque control
• Speed control
• Position control
• Fault monitoring
• Protective functions
Alarm and Error Codes (SGDH Sigma II)
| Alarm | Error Name | Meaning | Action |
|---|
| A.08 | Linear Scale Setting Error | Scaling fault | Check parameters |
| A.09 | Dividing Ratio Error | Incorrect encoder resolution | Check parameter settings |
| A.33 | Wrong Input Power | Incorrect supply voltage | Check power supply |
| A.55 | Linear Motor Speed Error | Speed parameter fault | Verify settings |
| A.76 | Pre-charge Contactor Failure | Pre-charge contactor fault | Check Servopack |
| A.90 | Excessive Position Error Warning | Excessive position deviation | Check mechanics |
| A.b1 | Reference Input A/D Error | Analog input fault | Check signal |
| A.C2 | Encoder Output Phase Error | Encoder fault | Check encoder |
| A.d1 | Full Closed Loop Error | Encoder value mismatch | Check feedback system |
| A.93 | Absolute Encoder Battery Low | Low battery voltage | Replace battery |
| A.94 | Data Setup Warning | Parameter fault | Check parameters |
| A.95 | Invalid Command Warning | Invalid command | Check controller |
| A.F5/A.F6 | Motor Disconnection | Motor connection fault | Check wiring |
The alarm codes originate from the uploaded Sigma II alarm documentation.
Preventive Recommendations for the Customer
• Regularly check brake function
• Monitor bearing noise
• Inspect the motor for dust contamination during maintenance
• Keep the encoder area clean
• Inspect seals regularly
• Monitor vertical axes for signs of dropping
• Replace worn brakes at the first signs of deterioration
Conclusion
This repair case clearly demonstrates that a defective holding brake can become much more than a simple mechanical issue. The resulting brake dust additionally damaged the encoder and ball bearings. By replacing the brake and overhauling both the encoder and bearings, the Yaskawa SGMGH-30DCA6H-OY was successfully restored to full operating condition. The axis now reliably maintains its position and the motor is prepared for many more operating hours.