24.08.2025 by Viktor Siebert
Mitsubishi MR-J2-20A AC Servo Drive, technical Analysis and Repair Case
We received two units of the MR-J2-20A that intermittently displayed the E9 alarm (ABS Servo On Warning).
This kind of sporadic error is challenging, as it does not appear consistently and is often triggered by unstable signals or component degradation.
Initial Inspection & Cleaning
Both units were opened and thoroughly cleaned. Dust and oil contamination were found, which are known to impair cooling and lead to unstable operation.
Component-Level Work
During the inspection, aged electrolytic capacitors and slightly oxidized connectors were identified. These were replaced preventively. The main control board (J2-P02F) was carefully checked and reconditioned. Special attention was given to the encoder communication circuits, as unstable signals can trigger E9 errors. Connector solder joints were reworked, and critical components were reinforced.
Testing & Validation
Both units underwent extensive testing on our CNC simulation bench. The test cycle included:
- Thermal stress tests under full load
- Repeated acceleration and deceleration cycles
- Positioning sequences with short intervals
- Long-duration runs to simulate real factory conditions
All processes were documented using detailed checklists and protocols.
Result: After preventive replacement and stabilization of critical parts, both units operated flawlessly. The intermittent E9 alarm could no longer be reproduced, confirming a reliable repair.
Preventive Measures for Customers
To extend the service life of the MR-J2-20A, we recommend:
- Regular cleaning of the drive and surrounding environment
- Fan replacement every 5–7 years to avoid heat accumulation
- Insulation measurements on motor cables to detect early ground faults
- Inspection of seals and cables, especially in humid or coolant-exposed environments
- Parameter checks after mechanical modifications to ensure stable servo gain settings
Conclusion
The Mitsubishi MR-J2-20A remains a robust and precise servo drive for CNC applications. As shown in this repair case, sporadic alarms like E9 are often related to aging components and unstable communication. With thorough refurbishment, preventive component replacement, and structured testing, the service life can be significantly extended.
For machine operators, this means: higher availability, fewer unexpected downtimes, and reduced overall costs.
To mentioned Mitsubishi Drive: Mitsubishi MR-J2-20A AC Servo Drive
More details about our Mitsubishi repair services can be found here:
Mitsubishi drive Repair by Industrypart
We regularly repair similar models, including:
MR-J10A
MR-J40A
MR-J70A
MR-J100A
MR-J200A
MR-J350A
Device Data
| Parameter | Value |
|---|
| Model | MR-J2-20A |
| Input Voltage | 3-phase 200–230 V, 50/60 Hz |
| Output Current | 1.5 A |
| Rated Power | 0.2 kW |
| Weight | approx. 1.0 kg (manual reference) |
| Cooling | Air-cooled |
| Type | AC Servo Drive, J2 series |
Operating Environment & Compatible Equipment
The MR-J2-20A is commonly used in CNC machines, machine tools, and manufacturing systems. It is often combined with Mitsubishi HF-series servomotors to ensure precise axis movements.
Recommended environment: 0–55 °C, dry, dust-free, low-vibration installation area.
Functional Description
The MR-J2-20A is a compact AC servo amplifier designed for accurate motor control. Main functions include:
- Position, speed, and torque control
- Integrated protective functions (overcurrent, overvoltage, overheating)
- Communication with CNC or PLC systems via pulse or analog inputs
- High-precision motion control for demanding industrial applications
Alarm Messages and Troubleshooting (extended)
| Alarm Code | Error Description | Cause | Solution |
|---|
| A.10 | Undervoltage | Power supply voltage too low | Check supply, stabilize voltage |
| A.11 | Board Error 1 | PCB failure | Replace servo drive |
| A.16 | Encoder Error 1 | Encoder signal failure | Check cable, replace encoder/motor |
| A.20 | Encoder Error 2 | Encoder communication error | Verify wiring, replace encoder |
| A.24 | Ground Fault | Earth fault at motor output | Inspect wiring, perform insulation test |
| A.30 | Regenerative Error | Brake resistor overload | Reduce load, check brake option |
| A.31 | Overspeed | Excessive speed | Adjust parameters, servo gain |
| A.32 | Overcurrent | Short-circuit or faulty power transistors | Check wiring/IPM |
| A.33 | Overvoltage | DC bus voltage exceeded | Check resistor, power supply |
| A.35 | Command Pulse Alarm | Input pulses too high/noisy | Adjust frequency, suppress noise |
| A.37 | Parameter Error | Incorrect/corrupted parameter | Adjust, replace drive if needed |
| A.46 | Motor Overheat | Thermal protection triggered | Reduce load, check environment |
| A.50/A.51 | Overload 1/2 | Continuous overload or blockage | Reduce load, inspect encoder |
| A.52 | Error Excessive (droop pulse) | Excess deviation detected | Adjust time constant, torque limit |
| A.8E | RS-232C Communication Error | Fault between drive and PC | Inspect cable, replace device |
| 8888 | Watchdog Error | CPU/board fault | Replace servo amplifier |
| A.E0 | Excessive Regeneration Warning | Regeneration >85% limit | Reduce load, stronger brake option |
| A.E1 | Overload Warning | Imminent overload | Reduce load, adjust tuning |
| A.E3 | Absolute Position Error | Fault in position transfer | Check wiring, PLC program |
| A.E5 | ABS Timeout Warning | Timeout during data transfer | Check program, wiring |
| A.E6 | Servo Emergency Stop | External emergency stop triggered | Remove cause, reset system |
| A.E9 | ABS Servo On Warning | Servo not switched on within required time | Check SON signal, PLC logic |
| A.EA | Servo On Warning | Servo ON signal error | Verify wiring, program |
Components
| Name | PCB Marking / Part Number | Quantity |
|---|
| Power & Control Board Assembly | J2-P02F or BC386A209G55A B | 1 |
| Power Section | Power Module | 1 |