16.02.2026 by Viktor Siebert
/ Repairreport Yaskawa AC Servo Motor SGMGH-30ACA6S
Initial Situation and Symptoms.
The motor arrived as a typical emergency case: insulation fault, intermittent drive shutdowns, and the characteristic smell of moisture inside an electrical machine.
The root cause became immediately visible:
The motor had completely drawn in coolant emulsion.
The contamination was not limited to the exterior. The emulsion had penetrated deep into:
- The winding chamber
- The bearing areas
- The encoder housing
Insulation measurements confirmed the critical condition.
We detected a short circuit between windings, and feedback signals from the encoder were unstable.
In such cases, there is a significant risk of damaging the servo amplifier if the issue is not resolved immediately.
Condition at Incoming Inspection
After complete disassembly, the full extent of damage became clear:
- Emulsion residues inside the housing
- Corrosion traces in the encoder area
- Reduced insulation resistance
- Phase-to-phase winding fault
- Encoder malfunction with signal dropouts
Important note:
Drying alone is not a solution. Coolant emulsion leaves conductive residues. If these remain inside the motor, the failure will reappear.
Disassembly and Structured Cleaning Process
The repair followed a defined industrypart workflow:
- Complete disassembly down to the winding chamber
- Mechanical pre-cleaning of all contaminated components
- Separation of electrical and mechanical assemblies
The cleaning process was performed in two stages:
- Degreasing and removal of emulsion films
- Residue-free rinsing process to eliminate conductive deposits
Controlled Drying and Electrical Recovery
A controlled multi-stage drying process was essential.
Moisture does not only remain on surfaces it penetrates insulation layers and capillary structures.
Our process included:
- Temperature-controlled drying cycles
- Intermediate insulation measurements
- Phase-to-phase and phase-to-ground verification
After stabilization of insulation values, the motor passed electrical acceptance limits.
Replacement of All Wear Components
Whenever a motor has drawn coolant, certain parts must always be replaced:
- All bearings
- All seals and O-rings
- Cable glands and sealing interfaces
- Encoder-related sealing components
The original encoder was beyond recovery and was replaced with:
Encoder UTSIH-B17CK
Encoder Installation, Adjustment and Programming
After mechanical installation, the following steps were performed:
- Electrical verification (supply voltage, signal stability)
- Mechanical alignment and positioning
- Parameter adjustment for operation with Yaskawa SGDH-30AE-OY
- Functional test under closed-loop control
Stable feedback is critical in Sigma II systems. Encoder faults typically trigger immediate alarm conditions.
Final Testing and Release
The motor was tested under real operating conditions:
- Warm-up cycle
- Acceleration and braking sequences
- Current consumption analysis
- Thermal behavior monitoring
- Extended endurance test
Only after stable performance under load was the motor released for operation.
Final Result
✔ Insulation values restored within specification
✔ Winding electrically stable
✔ Complete bearing replacement
✔ New encoder UTSIH-B17CK installed
✔ Stable operation with SGDH-30AE-OY
✔ Full load test passed
The motor was successfully returned to production-ready condition.
formation 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.
Yaskawa AC Servo Motor SGMGH-30ACA6S
System: SGDH-30AE-OY (Sigma II)
IDENTIFICATION
Manufacturer: Yaskawa Electric
Series: Sigma II
Motor Type: SGMGH-30ACA6S
Production Date: 04/2001
Serial Number: B0041F843210002
Country of Origin: Japan
NAMEPLATE DATA
| Parameter | Value |
|---|
| Rated Power | 2.9 kW |
| Rated Torque | 18.6 Nm |
| Rated Speed | 1500 rpm |
| Rated Voltage | 200 V |
| Rated Current | 23.8 A |
| Duty Cycle | Continuous (CONT.) |
| Insulation Class | F |
SYSTEM CONFIGURATION
Servo Amplifier: Yaskawa SGDH-30AE-OY
Voltage Class: 200 V
Control Type: Sigma II Digital Servo
Encoder (after repair): UTSIH-B17CK
Feedback Type: Incremental
FAILURE DESCRIPTION
- Insulation breakdown
- Coolant emulsion ingress
- Phase-to-phase short circuit
- Encoder failure
- Corrosion inside feedback housing
TYPICAL SIGMA II (SGDH) SERVICE-RELEVANT ALARMS
| Alarm Code | Description | Typical Cause |
|---|
| A.10 | Overcurrent | Short circuit / mechanical blockage |
| A.30 | Regeneration Fault | Brake resistor / DC bus issue |
| A.40 | Main Circuit Voltage Fault | Supply instability |
| A.C8 | Absolute Encoder Fault | Data inconsistency |
| A.C9 | Encoder Communication Error | Cable or encoder failure |
| A.CA | Encoder Parameter Error | Configuration mismatch |
| A.Cb | Encoder Echo Back Error | Feedback signal disturbance |