Mitsubishi Electric MELSERVO-J4 (MR-J4) troubleshooting
MELSERVO-J4 (MR-J4) is Mitsubishi Electric’s servo amplifier series for -A (pulse/analog), -B (SSCNET III/H), -GF (CC-Link IE Field) and multi-axis MR-J4W units. Alarms and warnings show as a two-digit number plus a one-digit detail number (for example AL.16.1). The detail number narrows the cause, so always record it.
Diagnose this with AI
Try Free Servo Diagnostic Upload a photo of the alarm screen, the fault history or a data export. InduQT compares the evidence and suggests the next useful checks.
How it reports faults
- The display shows the alarm or warning number with its detail number, for example [AL. 50.1]. The MR-J5 series later changed to three digits plus detail.
- Each alarm has a stop method (DB, EDB or SD) and lists whether it is cleared by alarm reset, CPU reset or cycling the power.
- On MR-J4-_A_ amplifiers, alarm codes can be output on ACD0–ACD2 by setting [Pr. PD34] to “_ _ _ 1”. Warnings ([AL. 90] to [AL. F3]) have no alarm code output.
- For overload and regenerative alarms (AL.30, AL.45, AL.46, AL.50, AL.51), Mitsubishi says to remove the cause and let the equipment cool for about 30 minutes before resetting.
Fault codes
| Code | Name |
|---|---|
| AL.16 | Encoder initial communication error 1 |
| AL.20 | Encoder normal communication error 1 |
| AL.25 | Absolute position erased |
| AL.33 | Overvoltage |
| AL.50 | Overload 1 |
| AL.51 | Overload 2 |
| AL.52 | Error excessive |
| AL.10 | Undervoltage |
| AL.12 | Memory error 1 (RAM) |
| AL.15 | Memory error 2 (EEP-ROM) |
| AL.17 | Board error |
| AL.1A | Servo motor combination error |
| AL.1E | Encoder initial communication error 2 |
| AL.1F | Encoder initial communication error 3 |
| AL.21 | Encoder normal communication error 2 |
| AL.24 | Main circuit error |
| AL.30 | Regenerative error |
| AL.31 | Overspeed |
| AL.32 | Overcurrent |
| AL.35 | Command frequency error |
| AL.37 | Parameter error |
| AL.45 | Main circuit device overheat |
| AL.46 | Servo motor overheat |
| AL.47 | Cooling fan error |
| AL.54 | Oscillation detection |
| AL.92 | Battery cable disconnection warning |
| AL.9B | Error excessive warning |
| AL.9F | Battery warning |
| AL.E0 | Excessive regeneration warning |
| AL.E1 | Overload warning 1 |
| AL.E6 | Servo forced stop warning |
Evidence to collect
- Photo of the display with the full alarm and detail number
- Alarm history from MR Configurator2
- Amplifier model (suffix -A, -B, -GF, W) and software version
- Servo motor model
- What the axis was doing at the alarm: power-up, servo-on, accelerating, constant speed, decelerating, stopped
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