19.08.2025 by Viktor Siebert
Mitsubishi MDS-B-SP-110 Spindle Drive Unit – Technical Analysis and Repair Experience
A customer contacted us after experiencing repeated Alarm 3B Power module overheat on their Mitsubishi MDS-B-SP-110 spindle drive. At first, the error appeared only sporadically and could be cleared by restarting the machine. But within a few weeks, the intervals shortened dramatically until the alarm occurred almost every five minutes. Production was no longer possible, and the customer faced increasing downtime.
When the unit arrived at our workshop, the first inspection already revealed typical signs of long-term wear: heavy contamination inside the housing, dust and coolant residues on the cooling fins, and a fan system that no longer delivered sufficient airflow. These factors are critical because the power module (IPM) generates significant heat during operation and depends entirely on effective cooling.
Repair process in detail:
- Initial diagnostics: We replicated the failure on our test bench and confirmed the thermal shutdown under load.
- Complete cleaning: The unit was disassembled, and all components were carefully cleaned using industrial-grade cleaning emulsions. Sensitive electronics were dried in a controlled oven to prevent moisture-related failures.
- Preventive replacement of critical components: Aging electrolytic capacitors, optocouplers, and semiconductors were replaced to ensure long-term stability.
- Power module inspection and replacement: Thermal stress tests confirmed degradation in the original IPM. The module was replaced with a fully tested part.
- Testing and validation: The repaired unit underwent extended trial runs on our in-house CNC simulation bench. We subjected it to thermal load tests under different operating conditions, verifying stability and performance over several hours of continuous operation.
- Documentation: Every step was logged with checklists and repair protocols, ensuring full traceability for the customer.
Result: The spindle drive was restored to full functionality and could be returned to service with confidence. For the customer, this repair avoided the high cost of replacing the complete unit and significantly reduced downtime.
Extended Preventive Measures for Customers
To extend the service life of spindle drives like the MDS-B-SP-110, we recommend a structured preventive maintenance approach:
- Regular cleaning: Remove dust and oil residues from cooling fins, air ducts, and circuit boards. Even thin layers of contamination reduce heat transfer and lead to higher internal temperatures.
- Fan replacement: Cooling fans are wear parts. They should be replaced every 3–5 years, even if they appear functional, since their performance gradually decreases.
- Seal inspection: Check and replace seals to prevent coolant, oil mist, or metal dust from entering the drive. These contaminants are among the most common causes of premature failures.
- Insulation resistance testing: Periodically measure insulation values of motor cables and connectors to detect moisture or insulation breakdown before a short circuit occurs.
- Thermal monitoring: Watch for rising operating temperatures in the drive. Increased heat is often the first indicator of fan degradation or clogged air passages.
- Preventive overhaul: Every 7–10 years, a complete overhaul is recommended, including replacement of capacitors, thermal interface materials, and other age-sensitive components.
By following these measures, customers can not only extend the service life of their spindle drives but also avoid costly production stops.
To mentioned Mitsubishi Drive: Mitsubishi MDS-B-SP-110 Spindle Drive Unit
More details about our Mitsubishi repair services can be found here:
Mitsubishi drive Repair by Industrypart
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Technical Summary of the Unit
| Parameter | Value |
|---|
| Type | MDS-B-SP-110 |
| Input Voltage | DC 283–311 V / AC 200–230 V, 50/60 Hz |
| Input Current | 41 A |
| Output Current | 37 A |
| Manufacturing Date | 1991/92 |
| Weight | approx. 12 kg |
| Manufacturer | Mitsubishi Electric, Japan |
Operating Environment & Compatible Systems
- Installed in CNC machine tools (e.g. Mazak, Mitsubishi-based controls)
- Compatible with medium-class spindle motors
- Typical environment: industrial workshops with dust, oil mist, and coolant exposure → demanding cooling and sealing conditions
Functional Description
The MDS-B-SP-110 is a spindle drive unit that supplies and controls the electrical power for spindle motors. Its main functions include:
- Power conversion and motor control via the integrated power module
- Speed, torque, and acceleration regulation
- Safety and protection functions (overcurrent, overvoltage, overheating)
- Communication with CNC control via encoder and signal lines
Alarm Messages and Troubleshooting
| Alarm | Error | Cause | Remedy |
|---|
| 12 | Memory error | RAM/ROM failure | Check or replace control board |
| 13 | Software process error | Data process not completed | Restart or reinitialize control |
| 17 | AD error | AD converter malfunction | Replace AD circuit |
| 21 | No signal (encoder) | Missing encoder feedback | Check encoder and cable |
| 23 | Excessive speed deflection | Large deviation between set/actual | Inspect mechanics, adjust control parameters |
| 31 | Overspeed | Motor exceeded maximum speed | Reduce load, verify settings |
| 32 | Power module overcurrent | Overcurrent in IPM | Check module, ensure proper cooling |
| 38 | Power module overheat | IPM overheated | Replace fan, improve cooling |
| 46 | Motor overheat | Motor overload or fan failure | Improve cooling, replace fan if necessary |
| 50 | Overload | Motor current exceeded limit | Reduce load, check cooling and ventilation |
Components
| Type | Board designation | Quantity |
|---|
| Control board | RK311B or BN634A817G51 | 1 |
| Power board | RK123B-SP-110 or BN634A804G51 | 1 |
| Power module | Integrated IPM power module | 1 |