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Mitsubishi MR-J2S-70B Servo Drive Unit Hauptbild
19.10.2025 by Viktor Siebert
Mitsubishi MR-J2S-70B Servo Drive Unit Alarm Code: AL-30 Regenerative Error / Brake Circuit Overload

Repair and Test Procedure at industrypart GmbH

The unit was received showing AL-30 on its display.
Visual inspection revealed heavy thermal stress around the regenerative brake resistor area. The resistor body showed discoloration, indicating long-term overload.
The cooling fan rotated irregularly, preventing adequate heat dissipation.

After disassembly, the power board J2SB-P11B and the power module section were examined.
A damaged regenerative IGBT transistor was detected.
The board was thoroughly cleaned and fitted with new transistors, driver optocouplers, and thermal sensors in the brake circuit.
An insulation test between P–C–D and chassis ground followed, together with a 1.5 kV high-voltage test for 60 seconds.

All critical parts in the power stage were replaced as a preventive measure.
The cooling fan was renewed and solder joints on the control board were reworked.
The amplifier was then tested on an original Mitsubishi test bench with various braking cycles and simulated load conditions.
After the repair, the unit operated stably, without overheating or further AL-30 alarms.


Preventive Measures

  1. Regular cleaning of fans and air ducts.
  2. Monitoring of braking frequency and machine parameter adjustment if needed.
  3. Use of an external brake resistor for high-frequency stop/start operation.
  4. Periodic check of P–C–D terminals for loose or oxidized contacts.
  5. Preventive replacement of fans and electrolytic capacitors every 4–6 years.

Conclusion

Alarm AL-30 on the Mitsubishi MR-J2S-70B is a typical failure related to the regenerative brake circuit.
Thermal overload and insufficient cooling often damage the transistor stage and brake resistor.
After replacement of the affected components, preventive overhaul and extensive testing under load, the drive was fully restored to reliable operation.
Stable regenerative braking, functional cooling and proper energy dissipation are essential to ensure long-term durability of this series.

More Info & Contact

To mentioned Mitsubishi Drive: Mitsubishi MR-J2S-70B Servo Drive Unit

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

We regularly repair similar models, including:
MR-J2S-70A
MR-J2S-70B4
MR-J2S-70B-QW219

Technical Specifications

General Description

The Mitsubishi MR-J2S-70B Servo Amplifier belongs to the J2-Super series (SSCNET version) and is widely used in precision automation and machine tool applications. With a rated output of 750 W and a compact design, it provides high reliability and dynamic performance.
The drive features integrated protection systems for overcurrent, overvoltage, overload, overheating, as well as regenerative and encoder errors.

Nameplate Data

SpecificationValue
ModelMR-J2S-70B
Power750 W
Input Voltage3 Ph + 1 Ph 200–230 V 50/60 Hz
Input Current3.8 A (3-phase) / 5.7 A (single-phase)
Output Voltage170 V 0–360 Hz 5.1 A
Control InterfaceSSCNET Bus
Protection ClassIP00 (open frame)
CoolingForced air cooling
WeightApprox. 1.7 kg
OriginMade in Japan

Compatible Servo Motors

The MR-J2S-70B can be combined with Mitsubishi HC-KFS, HC-MFS and HC-SFS motor series (for example HC-SFS52, HC-MFS73, HC-KFS73).
All motors in this series use absolute encoders with a resolution of 131 072 pulses per revolution.


Components

NameBoard DesignationQuantity
Power and Control Board AssemblyJ2SB-P11 / J2SB-P11B1
Power Module SectionPower Unit1

Typical Operating Environment

The amplifier is used in CNC machines, milling systems, positioning tables and packaging lines, normally connected via SSCNET to a Mitsubishi motion controller.
Permitted ambient temperature range: 0 – 55 °C, relative humidity ≤ 90 % (non-condensing).


Functional Description

The MR-J2S-70B precisely controls torque, speed and position of the connected servo motor using sinusoidal PWM modulation.
During deceleration, the excess kinetic energy of the motor is converted into heat through the regenerative resistor. If its thermal capacity is exceeded, the drive issues alarm AL-30.
Internal monitoring circuits continuously check current, voltage, temperature and SSCNET communication integrity.

ALARM TABLE – Mitsubishi MR-J2S-B Series (e.g., MR-J2S-70B)

CodeError NameDefinitionTypical CausesCorrective / Reset Action
10UndervoltagePower supply voltage too lowPower supply drop below 160 V (200 V unit) or 280 V (400 V unit), input power fluctuation, defective supplyCheck line voltage, stabilize input, reset by power cycle or reset signal
12Memory Error 1RAM failureFaulty control PCB componentsReplace servo amplifier
13Timer ErrorInternal timer faultController or CPU board malfunctionReplace amplifier
15Memory Error 2EEPROM failureMemory hardware defectReplace amplifier
16Encoder Error 1Communication lost between encoder and amplifierLoose or defective CN2 connector, broken cable, encoder failureCheck cable and connector, replace encoder or drive
17Board ErrorCPU or board malfunctionShort circuit or hardware faultReplace servo amplifier
19Memory Error 3RAM faultHardware malfunctionReplace drive
1AWrong Servo MotorIncompatible motor connectedWrong combination of drive and motorConnect matching type
20Encoder Error 2Encoder communication errorEncoder defective, wiring break or shortRepair cable or replace encoder
24Power Circuit FaultLeakage or short between main circuit and groundWrong wiring of TE1 (P/U/V/W), low insulation resistance, damaged power moduleCorrect wiring, replace faulty cable or module, reset after fault cleared
25Absolute Position LostAbsolute data lostBattery voltage low, battery disconnected, encoder capacitor dischargedReplace battery, check wiring, perform home return
30Regenerative OverloadBrake circuit overloadWrong brake resistor, too frequent braking, failed transistor or fanCheck resistor and wiring, replace damaged components, allow to cool, reset
31OverspeedMotor speed exceeded limitExcessive accel/decel ramp, unstable system, encoder errorAdjust ramp time, tune control loop, inspect encoder/motor
32OvercurrentCurrent exceeds rated valueShort between U/V/W, motor ground fault, damaged output stageEliminate short, repair or replace amplifier, reset
33OvervoltageDC bus voltage exceededMissing or wrong brake resistor, power surgesCheck brake resistor, inspect supply voltage stability
34CRC ErrorCommunication checksum errorBus cable not connected or damaged, noise interferenceReconnect or shield bus, add termination resistor
35Input Frequency Too HighInput pulse frequency exceeds specIncorrect program parametersReduce command frequency
36Transmission ErrorBus or board communication errorBus not connected, board defectiveCheck network wiring or replace drive
37Parameter ErrorOut-of-range parameterIncorrect setting or memory errorCorrect parameters or replace drive
45Power Unit OverheatPower stage temperature too highBlocked airflow, fan failure, high ambient temperatureRestore cooling, keep cabinet <55 °C, allow cooling and reset
46Motor OverheatMotor thermal limit exceededOverload, poor ventilation, defective thermistorReduce load, check air flow, ensure mechanical freedom
50Overload 1Output current exceeded rated valueMechanical overload, unstable loop, wiring or encoder faultReduce load, retune drive, check connections
51Overload 2Max. output current exceeded for several secondsMechanical overload, loose wiring, unstable operationVerify mechanics, re-adjust limits and control, fix fault
52Excessive ErrorFollowing error beyond limitAccel/decel too sharp, small “in-position” value, mechanical impact, encoder errorIncrease tolerance, reduce ramp, check mechanics/encoder
8ESerial CommunicationSSCNET communication errorCable fault, mismatch with controllerInspect SSCNET wiring and compatibility
88WatchdogCPU supervision errorInternal microprocessor faultReplace servo amplifier

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