A customer sent us a Mitsubishi MDS-B-CVE-260 Power Supply Unit that repeatedly triggered Alarm 01 (Overcurrent) whenever the machine was running under higher load. At first glance the unit seemed to be working, but the failure occurred sporadically and caused sudden production stops when full machine capacity was required.

Previous repair by a competitor

After contacting the customer, it turned out that the unit had already been serviced by another repair provider. The competitor had replaced the transistor module and some capacitors. The price was very attractive, but the truth was: after only three months the unit showed exactly the same error again.

First inspection

When we opened the device, the situation was immediately obvious:

• The transistor module was not new, but clearly a used component.
• The soldering work looked disastrous, as if done with a hammer rather than with precision.
• Some capacitors were replaced incorrectly: 47 µF / 50 V had been swapped with 47 µF / 220 V, which is absolutely unacceptable.
• The entire unit was dirty, the cooling fan rotated irregularly and sometimes stopped completely.

The real cause

Detailed measurement revealed the real problem:

• Out of 15 high-voltage buffer capacitors, 2 were completely dead, and the rest were already in a critical condition.
• This led to DC bus voltage instability under load, which directly triggered the overcurrent alarms.

Repair process

1. Complete cleaning removal of dust, oil and dirt deposits; fans checked and replaced.
2. Replacement of all buffer capacitors 15 pieces, correctly soldered and documented.
3. New transistor module installed using a verified original part.
4. Control board reworked poor soldering corrected, critical components replaced.
5. Checklists and documentation every step logged with measurement values in our system.
6. Load test on our test bench different operating scenarios simulated, from partial load to full load, with monitoring of temperature, signals and response times.

Why we put in this effort

At first glance, one might think that a repair with just a few replaced components would be sufficient. But this is exactly where the difference lies: a “quick fix” may appear to save money, but in reality it carries a significant risk. If the power supply fails again shortly after, the consequences are severe: unplanned machine downtime, production losses, delivery delays, and in the worst case the loss of important contracts.

One hour of downtime on a modern CNC machine can easily cost anywhere from several hundred to several thousand euros. Compared to that, the effort we put into our repairs, complete cleaning, preventive replacement of all critical components, documented tests and test protocols, is an investment in operational safety and reliability.

We see it as our responsibility to restore units in such a way that our customers can truly rely on their production. The extra effort is worthwhile not only from a technical perspective, but above all economically, because it significantly reduces total costs in the long run.

To mentioned Mitsubishi Drive: Mitsubishi MDS-B-CVE-260 Power Supply Unit

More details about our Mitsubishi repair services can be found here:
Mitsubishi drive Repair by Industrypart

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Technical Specifications

Application Environment & Compatible Devices

• Typical Machines: CNC machining centers, milling machines, turning machines.
• Controllers: Mitsubishi CNC controllers from MDS-B and MDS-C series.
• Compatible Units:
  • Servo Drive Units (e.g. MDS-B-V1, MDS-B-V2)
  • Spindle Drive Units (e.g. MDS-B-SP-185, MDS-C1-SPM-110)
  • Motors: Mitsubishi AC servo and spindle motors requiring DC bus supply

Functional Description

The MDS-B-CVE-260 is the central power supply unit within Mitsubishi CNC drive systems. Its functions include:

• Rectification & DC link voltage supply from AC input.
• Supplying multiple axes through the common DC bus.
• Regeneration of braking energy back into the grid.
• Protection mechanisms against overcurrent, overvoltage, ground faults, overheating.
• Monitoring & diagnostics via alarms, LEDs and communication with CNC.

Alarms & Troubleshooting

Components