The Yaskawa Servopack SGDV-120A01AY101AA was received with alarm codes A.710 and A.910. According to the customer, the affected axis exhibited highly unstable behavior. The motor only started jerkily, responded with delay to motion commands, and stopped again after a few seconds. In several cases, the two alarm codes alternated immediately after power-up or after short movement attempts.

After connecting the servopack to our Yaskawa Sigma V test bench, the behavior was reproducible. Already during the first functional test via SigmaWin, the motor showed pronounced instability. The motor reacted briefly in both directions but was unable to establish a stable rotation. It was noticeable that the control system was constantly compensating for an internal deviation.

The next step involved targeted current measurements on all three motor phases. This revealed a clear and unambiguous result. While phases U and V each carried approximately 4 A, phase W showed only about 0.8 A. Such a severe asymmetry is not permissible in a properly functioning servopack and inevitably leads to control instability.

This phase current fault also explains the observed behavior via the CN1 control interface. The controller sends correct motion commands, but the power stage cannot fully implement them due to the defective phase. The motor receives a distorted rotating field, begins to jerk, and is subsequently shut down by the servopack’s protection functions. As a result, alarms A.710 and A.910 are triggered.

After opening the unit, the power stage was examined in detail. The suspected internal fault in the phase W section was confirmed. The drive circuitry for this phase was no longer operating correctly, preventing proper current build-up. Such damage is often caused by long-term thermal stress, sporadic overload conditions, or pre-existing mains disturbances.

As part of the repair, the affected power stage was professionally restored and all relevant current paths were thoroughly checked. In addition, a preventive overhaul of adjacent assemblies was carried out to eliminate potential secondary failures. After completion of the repair, the servopack was tested again on the test bench.

The subsequent endurance test showed a clean and symmetrical current pattern on all three phases. The motor ran smoothly, evenly, and without control deviations. Movements via SigmaWin as well as via the CN1 control interface were executed stably. No further alarms or warnings occurred.

Preventive Measures for the Customer

Regular inspection of cooling and fan operation
Visual inspection of power terminals for thermal damage
Avoidance of continuous overload during operation
Regular preventive refurbishment of aging servopacks
Verification of mains quality and protection

Conclusion

This repair case clearly demonstrates how critical proper phase symmetry is in servo drive systems. Even a weakened or failed phase leads to unstable motor operation and recurring alarms. Through professional repair of the power stage and preventive refurbishment, the Yaskawa Servopack was fully restored and reliably returned to productive operation.

Information about the mentioned Servopack: Yaskawa Servopack SGDV-120A01AY101AA

Further details on our Yaskawa repairs can be found here: Yaskawa Sigma V Repair

📞 Feel free to contact us if you have any questions regarding your Yaskawa drive technology. Our team will be happy to assist you.

Technical Specifications

Application Environment and Compatible Devices

The Yaskawa SGDV-120A01AY101AA is typically used in CNC machine tools, automation systems, packaging machines, as well as handling and feeding systems.
It is designed for operation with Yaskawa Sigma V servo motors in the power range up to approximately 1.5 kW and is frequently used in axis applications with high requirements for dynamics, control accuracy, and positioning precision.

Typical application environments are industrial production systems with cyclic operation, frequent acceleration and deceleration, and varying mechanical loads. In these applications, the power electronics are exposed to significant thermal and electrical stress over many years.

Functional Description

The servopack converts the supply voltage into a controlled three-phase output voltage for precise servo motor control.
Integrated current, voltage, and temperature monitoring continuously supervises all three motor phases. Current control is performed on a per-phase basis, which means that even small deviations between phases can result in control instability, irregular operation, or protective shutdowns.

Communication with the higher-level control system is handled via the CN1 connector, while motor power and feedback are connected through separate power and encoder interfaces. Internal protection functions detect overcurrent, phase failure, overload, control deviations, and internal hardware faults, which are reported via defined alarm codes.

Alarm Messages and Troubleshooting

Components