When the Yaskawa SGMGH-20ACA6S arrived, the first visual impression already indicated a serious condition. The housing surface was heavily contaminated with dried coolant, metal particles and dark deposits across the entire frame. Moisture traces were visible at the terminal box and rear bearing cover.
The initial insulation test confirmed what the exterior suggested: the values were far below the acceptable range, indicating moisture ingress or weakened insulation layers.

The customer reported that Yaskawa had already inspected the motor and classified it as non-repairable. The recommended solution was a full retrofit, including replacement of the motor, servopack, cables and parts of the machine control. For many operators of older but reliable machinery, such a proposal would make the continued operation economically impossible. This was the reason why the case reached us through recommendation.

We began with full disassembly. Inside the rear housing we found clear evidence of long-term moisture exposure. Both the winding surfaces and the internal cable sections showed contamination and conductive residues. Although the winding itself was structurally sound, the insulation was severely compromised, explaining the very low insulation readings.

The UTSIH-B17CK encoder was also damaged. Several areas of the internal electronics showed corrosion and reduced signal quality. With high-resolution serial feedback, even minor deviations lead to communication faults, unstable positioning or complete loss of control. In this case the encoder was unquestionably defective.

After mechanical cleaning, the stator was dried in a controlled oven cycle for many hours. A subsequent 500-V insulation test showed improvement, but not enough. Only after additional resin treatment and reworking certain internal lead sections did the insulation reach levels comparable to a new motor.

The rotor was cleaned and its magnetic condition verified. The bearings were replaced to restore long-term reliability.
A new UTSIH-B17CK encoder was installed, aligned and initialized on our own Sigma-II test platform. Every encoder replacement requires proper signal verification, absolute position processing and full multi-turn test execution.

After reassembly, the motor was transferred to the SGDH-20AE-OY test bench. Multiple cycles followed:

• Torque-load verification
• Ramp 0–1500 rpm
• Artificial inertia load simulation
• Thermal stability monitoring
• Encoder feedback consistency checks

The motor ran immediately stable, without jitter, missing pulses or thermal irregularities.
The final insulation measurement confirmed the success: values at the level of a brand-new unit.

For the customer the economic result was significant. The proposed factory retrofit would have cost roughly ten times the repair amount while extending machine downtime by weeks. Our repair returned the machine to production in one week and prevented the scrapping of an otherwise valuable CNC system.

Präventive Maßnahmen

• Perform insulation tests every 6 to 12 months
• Inspect cables and connectors for moisture
• Clean and seal the terminal box
• Protect encoder housing and rear bearing cover
• Improve ventilation in humid environments
• Check seals and replace them when hardened

Fazit

This case demonstrates that even severely contaminated and moisture-damaged servo motors can be restored economically. The customer avoided excessive costs and preserved full machine productivity.

Information about the mentioned Servopack and Servomotor:

• Yaskawa SGMGH-20ACA6S AC Servo Motor
• Encoder Yaskawa UTSIH-B17CK
• Yaskawa SGDH-20AE-OY Servopack

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

Operating Environment and Compatible Devices

The motor is used in CNC machining centers, milling machines, gantry systems, metal cutting applications and general automation.
Typical axis assignments include X, Y, Z or auxiliary linear axes.
It is compatible with Yaskawa Sigma II SGDH-20AE servopacks.
It is commonly installed in machines from Mori Seiki, Okuma retrofits, Mazak and other CNC integrations.
Suitable for dry, humid or moderately contaminated environments when routine cleaning is performed.

Function

The SGMGH-20ACA6S is a high-performance AC servo motor of the Sigma II family.
It delivers precise positioning through its serial high-resolution feedback encoder UTSIH-B17CK.
The SGDH-20AE-OY servopack controls torque, speed and position in a closed-loop system and continuously monitors:

• Overcurrent
• Overheating
• Encoder communication
• Insulation condition
• Mechanical overload and axis blockage

Its high-resolution feedback enables accurate axis motion even with high inertia loads.

Alarms and Troubleshooting (SGDH) – Top 10 Codes

Components