Initial situation and fault description.

The Mitsubishi Servo Drive Unit MDS-C1-V1-35 was sent in by the customer due to abnormal motor noise during operation. In addition, the CNC control reported Alarm 32, which indicates an overcurrent condition in the power module.

According to the customer, the motor noise occurred shortly after axis activation and increased under load. The axis had previously operated without noticeable issues, and the fault appeared suddenly during normal production.

Initial assessment and typical causes

Alarm 32 on Mitsubishi MDS-C1 servo drives is a serious indication related to the power stage. In practice, this alarm is frequently associated with:

• axis overload conditions
• insulation issues at the motor
• internal defects within the power stage
• age-related degradation of electronic components

Because mechanical motor noise was reported at the same time, both the servo drive and the interaction between drive and motor had to be considered during diagnosis.

Incoming inspection and visual check

After receipt of the unit, a detailed visual inspection was performed.
No burn marks, visible damage, or contamination were detected. Connectors, power terminals, and the housing were in proper condition.

The unit was then prepared for further diagnostic testing.

Testing on the servo test system

The MDS-C1-V1-35 was operated on our CNC-like servo test system in order to reproduce the fault under controlled conditions.

During the first test runs, irregularities in the current behavior of the axis became apparent. Under load, unstable control states occurred, which were clearly audible as motor noise. Shortly thereafter, Alarm 32 could be reproduced reliably.

This confirmed that the root cause was not limited to the motor or cabling but was located within the servo drive itself.

Diagnosis and root cause

Detailed analysis revealed abnormalities in the power section of the servo drive.
Due to aging and long-term thermal stress, internal characteristics of the power electronics had drifted over time. This resulted in distorted current measurement signals and unstable motor control.

Such conditions can lead to increased current peaks, which trigger the overcurrent protection. At the same time, the motor may produce audible noise even though no mechanical defect is present.

Repair work performed

As part of the repair, the MDS-C1-V1-35 was completely disassembled and professionally cleaned.
The control and power assemblies were tested individually, critical areas were reworked, and the power stage was refurbished.

Special attention was paid to restoring stable current measurement and proper power stage control. The objective was to reestablish the original control stability of the servo drive.

Firmware, software, and customer-specific parameter settings remained unchanged throughout the entire repair process.

Final testing and result

After completion of the repair, the unit was retested on the servo test system.
The motor now operated smoothly and quietly, both at idle and under load. The previously reported motor noise was completely eliminated.

Extended test cycles confirmed stable control behavior, and Alarm 32 no longer occurred.
Only after successful long-term testing was the servo drive released for return shipment to the customer.

Conclusion

This repair case demonstrates that motor noise combined with Alarm 32 does not necessarily indicate a defective motor. In many cases, the root cause is located within the servo drive itself, particularly in the power electronics.

A focused electronic diagnosis and realistic load testing are essential to avoid unnecessary motor replacement and to identify the true source of the problem.

To mentioned Mitsubishi Drive: Mitsubishi Power Supply Unit MDS-C1-CV-75

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Mitsubishi drive Repair by Industrypart

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Application Information

The Mitsubishi MDS-C1-V1-35 Servo Drive Unit is typically used in CNC machine tools such as machining centers, lathes, and special-purpose machines.
It is designed for feed axes requiring precise speed and position control and is commonly paired with Mitsubishi AC servo motors from the HF and HA series.

Typical environments include production systems with continuous operation, frequent acceleration and deceleration cycles, and varying mechanical loads. In such applications, long-term thermal stress can contribute to aging effects within the drive electronics.

Alarm Messages and Troubleshooting

Alarm Table Mitsubishi MDS-C1-V1-35

Technical Information Mitsubishi MDS-C1-V1-35

Technical Specifications

Main Components