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At first glance, everything seems fine.
Even the type designation has been adjusted to 400V.
Measurably, the winding resistance of the UVW phases gave different values compared to an original motor.
Complete overhaul of the motors

Procurement of 10 Yaskawa SGMPH-04DAA21D motors

A customer had ordered 10 Yaskawa SGMPH-04DAA21D motors from us, as these were no longer available from the machine manufacturer and Yaskawa itself. We were aware that we had to do a lot of research to get the ordered models to our customer. Finally, there was an Asian dealer who offered the requested models for sale.

So far everything was fine from our point of view, the goods arrived on time and looked new at first sight. The packaging as well as the design had given a professional impression. We did not have much experience with the SGMPH-04DAA21D model yet, but thats usually not a problem for our technicians. Consequently, a corresponding test station was developed and assembled.

The motors basically worked, but our technicians immediately noticed unusual noises. We disassembled some models and it turned out that the noises were caused by a worn ball bearing.

We had already anticipated that there would be potential problems with this model and accordingly equipped the spare parts warehouse with encoders and new ball bearings.

The motors were then all overhauled, cleaned as well as painted and delivered to the customer. After about 2 weeks, the customer contacted us with a serious problem. He had tried to put the motors into operation, but he could not connect them mechanically. As a result, the customer compared the power connectors with originals and found that they did not match. Consequently, our technicians measured and documented an original motor with 200V and 400V, as well as the winding resistance of the UVW phases. The winding resistance for an original 200V version motor is approximately 3 x 2.0R and for 400V motors is approximately 3 x 7.5R. It turned out that the motors from the Asian dealer, who stated in the type designation that they would be 400V motors, were only 200V motors. In our customers case, everything was original and at this point we realized that we may have been victims of fraud. Our customer returned the goods.

As a result, we unfortunately had to inform our customers that we could not deliver the requested goods. So we tried to find a suitable and satisfactory solution. The customer still had other motors in stock, which he could use for his machines. Finally, we agreed with the customer on an alternative solution and repaired the stored motors. On the motors themselves, only the stator and rotor were functional, the rest, such as encoders, cables, connections, etc., had to be replaced. After the complete overhaul, we delivered the motors to the customer, who then reported a successful start-up and we were definitely one experience richer.


If the customer continued to try to keep the motors in use, consequential damage would be inevitable. The winding of the motors had a much lower resistance value than originally specified. This could overload the servo amplifier and, in the worst case, cause it to fail due to overheating or start fires on neighboring components.

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