Initial Condition.

The received MDS-B-SPJX2-22 spindle module shut down immediately after machine power up with alarm 10 undervoltage. The customer reported that the machine sometimes started without issues, while on other days the module stopped immediately. This sporadic pattern typically indicates a developing fault in the DC link or the internal charging circuitry.

At arrival the module showed minor contamination in the airflow area but no mechanical damage. Based on the symptoms the suspicion was directed toward an unstable DC link, either caused by aged capacitors or contact issues in the input section.

Diagnosis

At our test stand the module was supplied through an MDS-B-CR power supply. Already during the first power up it was evident that the DC link voltage did not rise as expected and remained below its nominal value. The charging time of the main capacitors exceeded the allowed threshold which correlates directly with alarm 10.

Further measurements revealed:

• deviating values on two DC link capacitors
• unstable current draw during the initial charging phase
• thermally fatigued solder joints in the inrush circuit
• slight oxidation at the DC bus connector area

Using a thermal camera we identified a hotspot at the inrush resistor, indicating an imbalanced current flow and an incipient failure.

Repair Procedure

The repair process began with a complete disassembly of the module. All power components were removed and individually tested. The DC link capacitors showed elevated ESR values, typical for aging and a common cause of undervoltage alarms.

The following work was carried out:

1. Replacement of the entire capacitor bank with industrial high temperature components.
2. Rework of all solder joints in the inrush and precharge section.
3. Cleaning of the heat sink, ventilation openings and internal chamber.
4. Inspection and cleaning of the gate drive board.
5. Testing of the IGBT module, no damage found.
6. Replacement of all DC bus connector contacts.
7. Final insulation test and functional measurement.

Test Operation

After the repair the module was tested across several temperature cycles. The DC link voltage built up stable and within specification. All protection systems responded correctly and the spindle ran through the full speed range without voltage drops. A continuous six hour runtime test showed no irregularities.

Conclusion

The customer received a fully overhauled module with all preventive components renewed. The fault was reproducibly eliminated and the unit is ready for reliable use.

Preventive Measures

• yearly cleaning of the airflow section
• inspection of mains quality and machine wiring
• regular insulation testing of spindle motors
• replacement of capacitors after ten to twelve years of operation
• checking DC bus connection points during maintenance
• verification of machine grounding

Summary

The MDS-B-SPJX2-22 modules are robust but sensitive to DC link fluctuations. Early maintenance and preventive replacement of thermally stressed components prevent undervoltage alarms and extend the lifetime of the entire drive system.

To mentioned Mitsubishi Drive: Mitsubishi MDS-B-SPJX2-22 Spindle Drive Unit

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Mitsubishi drive Repair by Industrypart

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Technical Specifications

Operating Environment and Compatible Devices

The MDS-B-SPJX2-22 is used in machining centers with Mitsubishi CNC controls, typically in combination with power supply units such as MDS-B-CR or MDS-B-CV and spindle motors of the HF or SJ series. It is used in machine tools, milling centers, lathes and special machines requiring high spindle dynamics and precise speed control. The module operates together with the power supply through the DC bus rails L+ and L minus and is referenced and monitored by the CNC control.

Functional Description

The spindle module converts the DC bus voltage from the power supply into three phase output current for the spindle motor. The internal vector control enables precise acceleration, positioning and braking of the spindle. Protection systems monitor DC bus voltage, output currents, IGBT temperatures, regeneration state and internal supply voltages. Alarm 10 indicates an undervoltage condition in the main circuit that can be caused by a defective power supply, high load peaks or internal charging failures.

Alarms and Troubleshooting

Components