29.08.2025 by Viktor Siebert
Mitsubishi FR-SF-4-7.5KP-T Spindle Drive Unit > Technical Analysis, Repair and Prevention
A customer from the Mediterranean region sent us two identical Mitsubishi FR-SF-4-7.5KP-T Spindle Drives at the same time. Interestingly, both devices showed the same alarm: a. 10 Under Voltage.
Analysis
Both spindle drives were installed in machines running continuous three-shift production under extremely high ambient temperatures. Over time, the heat stress had accelerated aging of electrolytic capacitors and weakened insulation in the power section. The cooling fans were heavily contaminated, further reducing the cooling capacity.
Repair Process
- Initial Diagnostics: Checking voltage supply, measuring insulation resistance, visual inspection of damaged boards.
- Complete Cleaning: Removing dust, grease, and dirt deposits, especially from cooling ducts.
- Preventive Replacement:
- Electrolytic capacitors
- Relays and power semiconductors
- Cooling fans and thermal fuses
- Control Board Check: Identifying signal processing errors, replacing defective ICs.
- Test Procedure: Running extended test cycles on a dedicated spindle drive test stand. Tests included thermal load cycles, regenerative braking and overspeed scenarios.
- Documentation: Full repair protocol and maintenance checklist were provided to the customer.
Result
Both repaired units successfully passed all endurance and thermal tests on our test machine. The customer was able to put the machines back into full operation, now with increased reliability thanks to preventive component replacement.
Preventive Measures for Customers
- Regular cleaning of cooling fans and filters
- Replacing fans every 3–5 years
- Periodic insulation measurements of the power stage
- Checking gaskets and seals to prevent dust accumulation
- Additional thermal monitoring in hot environments
Conclusion
This case study shows clearly: in hot climates and in continuous multi-shift operation, the risk of premature failure increases significantly. Through professional overhaul and preventive maintenance, the service life and operational reliability of spindle drives can be greatly extended, helping customers avoid costly machine downtimes.
To mentioned Mitsubishi Drive: Mitsubishi FR-SF-4-7.5KP-T Spindle Drive Unit
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Technical Summary of the Unit
| Property | Value |
|---|
| Model | FR-SF-4-7.5KP-T |
| Code | BN408U730 |
| Power | 7.5 kW |
| Rated Current | 22 A |
| Input Voltage | 380–460 V AC, 3~ |
| Control Power Supply | RS 220 V AC |
| Main Power Supply | RST 400 V AC |
| Frequency | 50/60 Hz |
Application Environment & Compatible Machines
The FR-SF-4-7.5KP-T Spindle Drive Unit is designed for demanding CNC applications. It is typically used in spindle systems of lathes, machining centers and other high-performance machine tools.
In regions with high ambient temperatures, such as the Mediterranean area, the unit is often exposed to continuous thermal stress and heavy-duty operation in multi-shift production.
Functional Description
This spindle drive ensures precise speed and torque control of the spindle motor. It provides safe operation by monitoring voltage, current, temperature, and signal consistency. Integrated protective features such as overcurrent, overvoltage, overspeed, and overheat detection prevent damage to the drive and the connected spindle motor.
Alarm Messages and Troubleshooting
| Alarm | Description | Cause | Solution |
|---|
| 10 | Under Voltage | Input supply voltage too low or momentary power loss | Check power supply, wiring and contacts |
| 12 | Memory Error 1 | Internal memory read/write failure | Inspect or replace control board |
| 15 | Memory Error 2 | Failure in 2-port communication | Check communication board |
| 21 | No Signal (Encoder) | No encoder signal detected | Check encoder, wiring, connectors |
| 23 | IC MAC 0.12 Error | Microchip failure | Replace IC or control board |
| 24 | Breaker Trip | Overcurrent in main circuit | Inspect power section, breakers |
| 25 | Over Current (Converter) | Current exceeded limit in converter | Inspect load, cooling, replace power section if needed |
| 26 | Phase Loss | One of the three input phases missing | Check input supply and wiring |
| 31 | Overspeed | Motor exceeded 115 % of rated speed | Adjust parameters, inspect load |
| 46 | Overheat (Motor) | Motor overheated due to overload or fan stop | Inspect cooling fan, reduce load |
Components
| Component | Model | Manufacturer No. |
|---|
| Control Board | SF-CH | BN634E266G52 |
| Communication Board | SF-TL | BN624A961G52A |
| Power Supply | SF-PWH | – |
| Power Module | 7.5k | – |