31.10.2025 by Viktor Siebert
Repair of a Mitsubishi FREQROL FR-SF-2-11KP-DC Spindle Drive Unit
Repair description.
The received unit exhibited two main issues: startup problems in cold condition and unstable speed regulation above approximately 2200 rpm. This kind of fault pattern is typical for aged components within the voltage and current sensing circuits as well as tolerance drift in the feedback electronics.
After initial inspection, the drive was completely disassembled and thoroughly cleaned. On the power board, thermal discoloration and several degraded electrolytic capacitors were found. The transistor modules showed significantly increased leakage currents, indicating semiconductor aging.
During the overhaul, more than 50 components were replaced, including capacitors, buffer and DC-link capacitors, current and voltage sensing modules, and driver elements in the control stage. The recalibration of feedback loops and reference voltages was particularly time-consuming, as these parameters directly affect speed stability.
After around 22 hours of repair work, the unit was tested on our Mitsubishi spindle test stand, paired with an original SJ spindle motor to simulate real load conditions. After several heating and speed cycles, regulation became completely stable across all ranges. The cold start issues did not reoccur.
Special attention was given to the thermal monitoring and discharge circuit inside the SF-PW power supply, which is a known weak point in older models. After replacement and calibration, the system’s response time improved noticeably.
A long-term test followed, lasting over 12 hours, with repeated acceleration and deceleration cycles. The drive passed all tests without any irregularities.
Service recommendations and preventive measures
For FR-SF series drives, preventive overhaul is recommended every 7–10 years. Common weak points include:
- Aging of electrolytic capacitors
- Contact issues on the SF-BS communication board
- Fan failures and thermal stress in the power module
- Parameter loss due to EEPROM degradation on the control board
Regular cleaning, thermal checks, and insulation testing are essential to maintain performance. Early inspection can prevent unexpected breakdowns, especially on machines with high spindle utilization and long duty cycles.
Conclusion
The repair of the Mitsubishi FR-SF-2-11KP-DC once again demonstrated that even older spindle drive systems can operate reliably and precisely after professional refurbishment. By replacing critical components and recalibrating the measurement circuits, the unit’s performance and stability were fully restored. The drive is now ready again for continuous industrial operation.
To mentioned Mitsubishi Drive: Mitsubishi FREQROL FR-SF-2-11KP-DC Spindle Drive Unit
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Technical Summary of the Unit
Overview
The Mitsubishi FREQROL FR-SF-2-11KP-DC is a high-performance spindle drive system designed for precise and dynamic applications in CNC machine tools. It operates in combination with Mitsubishi SJ spindle motors and is characterized by accurate speed control, stable power output, and a modular structure. The FR-SF series represented a significant technological milestone in the 1990s for high-speed spindles, particularly in mid- and high-end machining centers.
The system consists of several functional modules responsible for control, power conversion, and communication. This modular design allows targeted maintenance of individual boards, which significantly increases the service life of the system.
Model designation
- FR = Frequency Inverter (FREQROL Series)
- SF = Spindle Frequency Converter
- 2 = 2nd Generation, 200 V Class
- 11KP = 11 kW rated power
- DC = DC power supply via external power module
Technical data
| Description | Value |
|---|
| Model | FR-SF-2-11KP-DC |
| Power | 11 kW |
| Input voltage | 200–230 V AC, 3-phase |
| Input current | approx. 55 A |
| Output voltage | max. 200 V AC |
| Frequency range | 0 – 400 Hz |
| Motor type | Mitsubishi SJ Series (e.g. SJ-286705K) |
| Insulation class | F |
| Ambient temperature | 0 – 40 °C |
| Cooling | Forced air |
| Protection class | IP20 |
| Control board | SF-CA |
| Power supply | SF-PW (old) or SF-PW30 (new) |
| Communication board | SF-BS |
| Power module | Power Unit 11K |
Components
| Type, DE | Spare Parts, ENG | Model designation | Quantity |
|---|
| Steuerplatine | Main Control Board | SF-CA | 1 |
| Netzteil | Power Supply | SF-PW (old) / SF-PW30 (new) | 1 |
| Kommunikationsplatine | Communication Board | SF-BS | 1 |
| Leistungsteil | Power Module | Power Unit 11K | 1 |
Application environment and compatible systems
The FR-SF-2-11KP-DC is mainly used in Mitsubishi-controlled CNC machines of the M500 and M600 series. Typical applications include high-speed spindles for milling machines, boring machines, and grinders.
In combination with an 11 kW spindle motor of the SJ series, the system achieves speeds above 4000 rpm while maintaining stable torque. The external power supply unit SF-PW allows the system to supply several spindle or axis amplifiers simultaneously.
Typical alarms and fault conditions
| Nr. | Code | Bezeichnung (Deutsch) | Beschreibung (Deutsch) | Code (Engl.) | Alarm Name (Englisch) | Description (English) |
|---|
| 10 | UV | Unterspannung | Tritt auf, wenn die Eingangsspannung unter den spezifizierten Wert fällt oder eine momentane Stromunterbrechung länger als 10 ms dauert. | UV | Under Voltage | This alarm occurs if input supply voltage goes down below the specified level, or if instantaneous power failure lasting for over 10 msec occurs. |
| 12 | ME1 | Speicherfehler 1 | Tritt auf, wenn beim Lesen oder Schreiben des internen Speichers ein Fehler erkannt wird. Der Speicher wird beim Einschalten geprüft. | ME1 | Memory Error 1 | This alarm occurs if read from, or write to internal memory for controller system control does not go normally (memory is checked when the controller is turned on). |
| 13 | CE | Externer Taktfehler | Tritt auf, wenn die Zugriffszeit des 2-Port-Speichers im NC-Modus außer Kontrolle gerät, z. B. durch Ausfall des externen Takts. | CE | External Clock Error | This alarm occurs if access time for 2 ports is out of control during NC mode, due to failure in external clock (when M300 series CNC is bus-linked with the controller). |
| 15 | ME2 | Speicherfehler 2 | Tritt auf, wenn der 2-Port-Speicher für die Datenkommunikation (bei Verbindung mit M300-Serie CNC) nicht ordnungsgemäß funktioniert. | ME2 | Memory Error 2 | This alarm occurs if 2-port memory for data communication (when FR-SF is bus-linked with M300 series CNC) does not function properly. |
| 17 | BE | Steuerungsplatinenfehler | Tritt auf, wenn ein Teil der Steuerplatine nicht in gutem Zustand ist oder nicht funktioniert. | BE | PC Board Error | This alarm occurs if any part of control card is not in good condition. |
| 20 | NS1 | Kein Signal 1 (PLG) | Tritt auf, wenn das Signal des im Motor eingebauten Encoders nicht auf normalem Pegel liegt. | NS1 | No Signal 1 (PLG) | This alarm occurs if signal from motor built-in encoder is not at normal level. |
| 21 | NS2 | Kein Signal 2 (Spindel-Encoder) | Tritt auf, wenn das Signal des Spindel-Encoders für orientierten Halt nicht erkannt wird oder ausfällt. | NS2 | No Signal 2 (Spindle Encoder) | This alarm occurs if signal from encoder for oriented spindle stop is not input, or not at normal level. |
| 22 | NSS | IC MAC012 Fehler | Tritt auf, wenn das IC „MAC012“ auf der Steuerplatine nicht ordnungsgemäß funktioniert. | NSS | IC MAC012 Error | This alarm occurs if IC “MAC012” of control card does not function properly. |
| 23 | OSE | Geschwindigkeitsabweichung | Tritt auf, wenn die Differenz zwischen tatsächlicher Motordrehzahl und Referenzgeschwindigkeit zu groß ist. | OSE | Error Excess (Speed) | This alarm occurs if difference between true motor speed and referenced speed is excessive. |
| 24 | BRT | Leistungsschalter ausgelöst | Tritt auf, wenn der Strom im Hauptstromkreis den spezifizierten Grenzwert überschreitet. | BRT | Breaker Trip | This alarm occurs if current exceeding the specified limit flows in the main (power) circuit. |
| 25 | COC | Überstrom (Konverter) | Tritt auf, wenn im Konverter ein Strom über den spezifizierten Grenzwert fließt. | COC | Overcurrent (Converter) | This alarm occurs if current exceeding the specified limit flows in converter. |
| 26 | PL | Phasenausfall | Tritt auf, wenn eine der drei Eingangsphasen ausfällt. | PL | Phase Loss | This alarm occurs if any one of three phases of input power supply fails. |
| 27 | CPUE | CPU-Fehler | Tritt auf, wenn ein arithmetischer Rechenfehler oder eine falsche Parametereinstellung auftritt. | CPUE | CPU Fault | This alarm occurs if error in arithmetic operation, due to improper parameter setting, occurs. |
| 31 | OS | Überspeed | Tritt auf, wenn die Motordrehzahl 115 % der maximalen Drehzahl überschreitet. | OS | Overspeed | This alarm occurs if motor speed exceeds 115% of the maximum motor speed. |
| 32 | OC | Überstrom (Inverter) | Tritt auf, wenn im Inverter ein Strom über den spezifizierten Grenzwert fließt. | OC | Overcurrent (Inverter) | This alarm occurs if current exceeding the specified limit flows in controller. |
| 33 | OV | Überspannung | Tritt auf, wenn die Spannung des Hauptkondensators aufgrund regenerativer Bremsenergie über den spezifizierten Grenzwert steigt. | OV | Overvoltage | This alarm occurs if voltage charged in main circuit capacitor goes up, due to regenerative brake energy, over the specified limit. |
| 34 | DP | Paritätsfehler | Tritt auf, wenn bei der Datenübertragung zwischen M300 CNC und FR-SF ein Paritätsfehler auftritt. | DP | Data Parity | This alarm occurs if parity check error occurs in data transmission between M300 series CNC and FR-SF (when FR-SF is bus-linked with CNC). |
| 35 | DE | Datenfehler | Tritt auf, wenn der von der CNC vorgegebene Bewegungsbefehl den spezifizierten Grenzwert überschreitet. | DE | Data Error | This alarm occurs if movement command specified by CNC exceeds the specified limit (when FR-SF is bus-linked with CNC). |
| 36 | TE | Datenübertragungsfehler | Tritt auf, wenn die Datenübertragung zwischen FR-SF und CNC nicht ordnungsgemäß funktioniert. | TE | Data Transfer Error | This alarm occurs if data transfer does not go satisfactorily (when FR-SF is bus-linked with CNC). |
| 37 | PE | Parameterfehler | Tritt auf, wenn der eingestellte Parameterwert außerhalb des zulässigen Bereichs liegt (wird beim Einschalten geprüft). | PE | Parameter Error | This alarm occurs if set parameter value is out of the permissible range (this check is made when the controller is turned on). |
Functional description
The FR-SF-2-11KP-DC spindle drive converts the three-phase AC supply voltage via the SF-PW power supply module into a stable DC bus voltage, which is then converted by the power unit into frequency-controlled AC voltage. This modulated output provides the spindle motor with precisely regulated voltage and frequency.
The SF-CA control board manages speed regulation, monitoring of feedback signals, and communication with the CNC control. The SF-BS board handles data exchange between the spindle drive and the main control system.
The system operates with high control response, ensuring smooth operation even at high rotational speeds. Faults in temperature compensation or current measurement circuits often lead to speed fluctuations or excessive corrections.