Guide · Mitsubishi · MELSERVO-J2S · MELSERVO-J3 · Updated November 2026
Mitsubishi MR-J2S and MR-J3 servo alarm list (absolute models)
MR-J2S and MR-J3 amplifiers with absolute position encoders show an alarm or warning number on the display. This page gives the numbers and names from Mitsubishi Electric's MR-J2S-A and MR-J3-A instruction manuals, with the cause in brief, for the series most often seen on older machines. The numbers differ from MR-J4, so use the list for your series. Star Automations is an independent repairer, not a Mitsubishi Electric authorised service provider.
First checks when the amplifier shows an alarm
- Note the alarm number and photograph the display. Check whether it is an alarm (stops the drive) or a warning.
- Read the amplifier label to confirm the series (MR-J2S or MR-J3) before using a table.
- Check the supply, the regenerative resistor, the cooling fan and the encoder cable.
- For AL.25, AL.92, AL.9F and AL.E3 check the absolute position backup battery and cable first.
- Switch off, wait until the charge lamp is off, and only then open the amplifier.
- After alarms 30, 45, 46, 50 and 51, remove the cause and allow about 30 minutes for cooling. Do not cycle the power repeatedly.
MELSERVO-J3 (MR-J3-A) alarm numbers
| No. | Alarm name | Cause in brief | Related guide |
|---|---|---|---|
| 10 | Undervoltage | Supply voltage low, momentary control-power loss, or amplifier fault. Check the supply first. | Guide |
| 12 | Memory error 1 (RAM) | RAM fault. Amplifier replacement or repair. | – |
| 13 | Clock error | Printed board fault. Amplifier replacement or repair. | – |
| 15 | Memory error 2 (EEP-ROM) | EEP-ROM fault, or more than about 100,000 writes. | – |
| 16 | Encoder error 1 (at power on) | Encoder connector, cable-type setting (PC22), cable or encoder fault, or noise. | Guide |
| 17 | Board error | CPU or parts fault. | – |
| 19 | Memory error 3 (Flash-ROM) | Flash-ROM fault. | – |
| 1A | Motor combination error | Amplifier and servo motor are not a valid combination. | – |
| 20 | Encoder error 2 (during runtime) | Encoder cable, oscillation with high acceleration, encoder fault or noise. | Guide |
| 21 | Encoder error 3 (during runtime) | Detection circuit error in the encoder. | – |
| 24 | Main circuit error | Ground fault on the U/V/W motor power: wiring, cable, motor, amplifier or dynamic brake. | – |
| 25 | Absolute position erase | Encoder supply voltage dropped: battery low or faulty, cable or encoder fault, or first power-on. | Guide |
| 30 | Regenerative error | PA02 setting, excessive regenerative load, regenerative option missing or faulty. Allow about 30 minutes to cool. | Guide |
| 31 | Overspeed | Command pulse frequency too high, short accel/decel time, unstable servo or encoder fault. | Guide |
| 32 | Overcurrent | Motor cable short or ground fault, dynamic brake, amplifier or motor fault, or noise. | Guide |
| 33 | Overvoltage | Regenerative option missing, wrong setting or wiring, or high supply voltage. | Guide |
| 35 | Command pulse frequency alarm | Pulse frequency too high, noise on the pulse line or command device fault. | – |
| 37 | Parameter error | Wrong or corrupted parameter, or EEP-ROM write limit reached. | – |
| 45 | Main circuit device overheat | High ambient temperature, debris on fan or heat sink, or repeated power cycling under overload. | Guide |
| 46 | Servo motor overheat | Motor ambient above 40°C, overload or faulty thermal sensor. | Guide |
| 47 | Cooling fan alarm | Fan life expired, foreign matter stopping the fan, or fan power failure. | – |
| 50 | Overload 1 | Continuous output above rating, unstable servo or encoder fault. Allow about 30 minutes to cool. | Guide |
| 51 | Overload 2 | Machine collision, wrong U/V/W connection, broken cable, encoder or motor fault. | Guide |
| 52 | Error excessive | Short accel/decel time, low torque limit, supply voltage drop, collision or encoder fault. | Guide |
| 8A | Serial communication timeout | Communication cable broken, cycle too long or wrong protocol. | – |
| 8E | Serial communication error | Cable or communication device fault, or wrong codes. | – |
| 88888 | Watchdog | Amplifier parts fault or CPU malfunction from noise. Showing 88888 only at power-on is not an error. | – |
Source: MR-J3-A Servo Amplifier Instruction Manual (SH-030038), troubleshooting chapter. Our linked guides were written for MR-J4 and the details can differ on MR-J3.
MR-J3-A warnings
| No. | Warning name | Cause in brief |
|---|---|---|
| 92 | Battery cable disconnection warning | Battery cable open, battery voltage about 3 V or less, or encoder cable broken. |
| 96 | Home position setting warning | Droop outside the in-position range during home setting, or creep speed too high. |
| 99 | Stroke limit warning | LSP or LSN switched off in the commanded direction. |
| 9F | Battery warning | Battery voltage at or below 3.2 V. Replace the battery. |
| E0 | Excessive regenerative warning | Regenerative power at 85% or more of the permissible level. |
| E1 | Overload warning 1 | Load at 85% or more of the overload alarm level. |
| E3 | Absolute position counter warning | Encoder pulse fault or noise, encoder fault, or travel beyond the revolution range. |
| E5 | ABS time-out warning | Ladder program or ST2/TLC wiring problem. |
| E6 | Servo emergency stop warning | EMG is off (external emergency stop). |
| E8 | Cooling fan speed reduction warning | Fan life expired, fan power broken or foreign matter in the fan. |
| E9 | Main circuit off warning | Servo-on given while main circuit power is off. |
| EA | ABS servo-on warning | SON turned on more than 1 s after entering ABS transfer mode. |
| EC | Overload warning 2 | Repeated excess current in U/V/W phases during stops. |
| ED | Output watt excess warning | Output wattage above 150% of rating in continuous operation. |
MELSERVO-J2S (MR-J2S-A) alarm numbers
| No. | Alarm name | Cause in brief | Related guide |
|---|---|---|---|
| 10 | Undervoltage | Supply voltage dropped. | Guide |
| 12 | Memory error 1 | RAM fault. | – |
| 13 | Clock error | Printed board fault. | – |
| 15 | Memory error 2 | EEPROM fault, or more than 100,000 EEPROM writes. | – |
| 16 | Encoder error 1 | Encoder communication error: connector, cable or encoder. | Guide |
| 17 | Board error | CPU or parts fault. | – |
| 19 | Memory error 3 | ROM memory fault. | – |
| 1A | Motor combination error | Amplifier and motor are the wrong combination. | – |
| 20 | Encoder error 2 | Encoder communication error, or excessive acceleration from oscillation. | Guide |
| 24 | Main circuit error | Ground fault at the U/V/W output. | – |
| 25 | Absolute position erase | Encoder absolute data lost: battery or super capacitor low, or first power-on. | Guide |
| 30 | Regenerative error | Regenerative power over the permitted value, wrong parameter 0, or faulty regenerative circuit. Allow about 30 minutes to cool. | Guide |
| 31 | Overspeed | Speed exceeded the permitted value: command frequency, accel/decel time, instability or encoder. | Guide |
| 32 | Overcurrent | Short or ground fault at the outputs, faulty IPM, noise or regenerative transistor fault. | Guide |
| 33 | Overvoltage | Converter bus voltage above 400 VDC. | Guide |
| 35 | Command pulse frequency error | Pulse frequency too high, noise or command device fault. | – |
| 37 | Parameter error | Parameters wrong or corrupted, EEPROM write limit, or conflicting settings. | – |
| 45 | Main circuit device overheat | Fan stopped, repeated power cycling under overload, or high ambient temperature. | Guide |
| 46 | Servo motor overheat | Motor ambient above 40°C, overload, thermal sensor, wrong connection or encoder. | Guide |
| 50 | Overload 1 | Load exceeded the overload protection characteristic. Allow about 30 minutes to cool. | Guide |
| 51 | Overload 2 | Machine collision or maximum current flowing for several seconds. | Guide |
| 52 | Error excessive | Position deviation exceeded 2.5 rotations (10 rotations for software older than B0). | Guide |
| 8A | Serial communication time-out error | Cable break, cycle longer than parameter 56, or wrong protocol. | – |
| 8E | Serial communication error | Cable or communication device fault. | – |
| 88888 | Watchdog | CPU or parts fault. | – |
Source: MR-J2S-A Servo Amplifier Instruction Manual (SH-030006), troubleshooting chapter. MR-J2S has no cooling fan alarm 47 and no fan speed warning E8.
MR-J2S-A warnings
| No. | Warning name | Cause in brief |
|---|---|---|
| 92 | Open battery cable warning | Battery cable open, or battery voltage about 3.2 V or less. |
| 96 | Home position setting warning | Droop above the in-position range, or creep speed too high. |
| 9F | Battery warning | Battery voltage 3.2 V or less. Replace the battery. |
| E0 | Excessive regenerative warning | Regenerative power at 85% or more of the permitted value. |
| E1 | Overload warning | Load at 85% or more of overload alarm 1 or 2 level. |
| E3 | Absolute position counter warning | Multi-revolution counter out of range: noise, encoder or travel beyond limit. |
| E5 | ABS time-out warning | Ladder program error or improper ST2/TLC wiring. |
| E6 | Servo emergency stop warning | EMG is off. |
| E9 | Main circuit off warning | Servo-on given while main circuit power is off. |
| EA | ABS servo-on warning | SON turned on more than 1 s after entering absolute data transfer mode. |
Amplifier, motor, cable or battery?
Encoder and absolute alarms (16, 20, 21, 25, 92, 9F, E3)
Check the encoder cable and connector, then the backup battery, then the encoder. See AL.16 and AL.20 and AL.25.
Overcurrent and ground fault (24, 32)
Disconnect the motor power cable and see whether the alarm stays. It can be the amplifier power stage, the cable or the motor. See AL.32.
Many of these alarms (fan, battery, capacitor) can be prevented by replacing parts on schedule. See Mitsubishi servo scheduled maintenance. For the MR-J4 list see Mitsubishi MR-J4 alarm list. If the alarm stays, see Mitsubishi servo drive repair, servo motor repair and encoder repair.
Look up one alarm quickly
Type the number from the display into the servo alarm lookup to see the name and cause for MR-J4, MR-J3 or MR-J2S.
Parts that cause alarms can be replaced on schedule
The Mitsubishi manuals give a service life for the cooling fan, the absolute position battery, the relays and the smoothing capacitor. Replacing them before they fail avoids alarms 47, E8, 25, 9F and 92 and unplanned stops. Star Automations can help with these replacements as part of our repair service. Details and intervals are on the scheduled maintenance page.
Questions
Do MR-J2S and MR-J3 use the same alarm numbers as MR-J4?
No. The three series share many numbers, but each has its own list. For example MR-J2S and MR-J3 have no alarm 11, 14, 1B, 1E or 1F, and MR-J3 adds alarms such as 21 and 47. Use the list for your series, and the manual for your exact amplifier.
What does AL.25 absolute position erase mean?
The amplifier has lost the absolute position data. The manuals list a low or faulty battery, a faulty encoder cable or encoder, and first power-on as causes. After fixing the cause the home position has to be set again.
What is the difference between AL.9F and AL.92?
Both relate to the absolute position backup battery. AL.9F is the battery warning (voltage at or below 3.2 V) and AL.92 is the battery cable disconnection or open-cable warning. Replace the battery on AL.9F; check the cable on AL.92.
Will replacing the battery erase the absolute position?
For MR-J3, the manual says replacing the battery with the control circuit power on does not erase the absolute position data, while replacing it with the control power off does, unless the backup procedure is followed. See our scheduled maintenance page.
Can I reset the alarm and restart straight away?
Not while the cause is still present. After alarms 30, 45, 46, 50 and 51 the manuals say to remove the cause and allow about 30 minutes for cooling.
Do you repair MR-J2S and MR-J3 amplifiers and servo motors?
Yes. Star Automations repairs Mitsubishi MELSERVO amplifiers, servo motors and encoders. We are an independent repairer and not a Mitsubishi Electric authorised service provider.
About the author
S. Suresh, Founder and CEO of Star Automations. More than 25 years in industrial electronics repair, with servo motor and drive repair as the main focus since 1998. Last updated: .
Send the alarm number and amplifier model.
WhatsApp a photo of the amplifier label and the display to +91 97866 22233, or email info@starautomations.com.