Guide · Mitsubishi · MELSERVO-J2S · MELSERVO-J3 · Updated November 2026
Mitsubishi servo scheduled maintenance: parts to replace and when
Mitsubishi Electric lists service lives for the cooling fan, the absolute position battery, the relays and the smoothing capacitor in its MR-J2S and MR-J3 amplifier manuals. Planning these replacements before they fail is cheaper than an unplanned stop. This page lists the parts by interval, with the figures taken from the manuals. Star Automations is an independent repairer, not a Mitsubishi Electric authorised service provider.
Parts to replace, by interval
| Interval | Part | What the manual says | Replace |
|---|---|---|---|
| Every periodic inspection | Terminal block screws, power and motor cables, connectors | Retighten loose terminal screws. Check cables for scratches and cracks. Do not test the amplifier with a megger. Listen for unusual noise from the servo motor bearings. | No parts replaced unless a fault is found |
| 10,000 to 30,000 hours (about 2 to 3 years) | Amplifier cooling fan | Mitsubishi gives this as the fan life and recommends replacement after a few years of continuous operation. MR-J3 can warn with AL.E8 (fan speed reduction) and alarm AL.47. | Cooling fan |
| Within 3 years of operation start (MR-J3 manual) | Absolute position backup battery (MR-J3BAT on MR-J3) | The MR-J3 manual says to replace the battery within three years of operation start, whether power is kept on or off. Battery life is five years from the date of manufacture, and backup time with power off is about 10,000 hours. Warnings AL.9F and AL.92 and alarm AL.25 relate to the battery. | Backup battery |
| 100,000 power-on and emergency-stop operations | Relays in the amplifier | The manuals give the relay life as 100,000 cumulative power-on and emergency-stop operations. A machine that is switched on and e-stopped often reaches this sooner. | Relays |
| About 10 years of continuous operation | Smoothing capacitor | The manuals give about 10 years of continuous operation at 40°C or less. Life depends strongly on ambient temperature and operating conditions. | Smoothing capacitor |
| Condition-based | Servo motor bearings | Mitsubishi does not give one fixed hour figure in the amplifier manuals we checked. The periodic inspection lists a check for unusual bearing noise. Replace bearings when noise, vibration or heat rises, or when the motor is repaired. | Motor bearings (when found worn) |
Sources: MR-J3-A Servo Amplifier Instruction Manual (SH-030038), sections on parts having service lives and the absolute position detection system; MR-J2S-A Servo Amplifier Instruction Manual (SH-030006), inspection chapter. Figures assume the operating conditions in the manuals. Check the manual for your exact amplifier.
Warnings that show a part is wearing out
Cooling fan
MR-J3: warning E8 (fan speed reduction) and alarm 47. On MR-J2S the fan is checked for noise or vibration at inspection. Overheat alarm 45 can follow a stopped fan.
Backup battery
Warning 9F (battery voltage 3.2 V or less), warning 92 (battery cable open) and alarm 25 (absolute position erase). Change the battery on 9F before 25 appears.
Encoder and counter
Warning E3 (absolute position counter) and alarms 16 and 20 can come from noise, cable or encoder faults. See the MR-J2S and MR-J3 alarm list.
Capacitor and relays
No warning is shown. Track the machine age, the temperature of the panel and the number of power-on and emergency-stop operations.
Replacing the absolute position battery
- Replace the MR-J3 battery within three years of operation start. Battery life is five years from manufacture.
- Replace it with the control circuit power on to keep the absolute position data. Replacing it with the power off erases the data unless the backup procedure is followed.
- Switch off the main circuit power and wait 15 minutes or longer before replacing the battery (20 minutes for 30 kW and above).
- If AL.25 appears, the home position must be set again.
Plan your own replacements
Enter the commissioning date in the servo maintenance planner to see the replacement window for each part, and send the list to Star Automations on WhatsApp.
How Star Automations helps
Send us the amplifier or servo motor with the label details. As part of repair or refurbishment we can replace the cooling fan, the backup battery, relays and capacitors, and replace worn motor bearings, and tell you which other parts are near the end of their life. Every repair is carried out by us as an independent repairer. See Mitsubishi servo drive repair, servo motor repair and encoder repair. If an alarm is already showing, use the MR-J2S and MR-J3 alarm list or the MR-J4 alarm list.
Questions
How often should the Mitsubishi servo amplifier cooling fan be replaced?
The MR-J2S and MR-J3 manuals give the cooling fan life as 10,000 to 30,000 hours, about 2 to 3 years, and recommend replacement after a few years of continuous operation. Replace it sooner if the fan is noisy or an alarm such as AL.47 or warning AL.E8 appears on MR-J3.
When should the absolute encoder battery be changed?
The MR-J3 manual says to replace the battery within three years of operation start whether power is on or off. For MR-J2S check section 15.2 of the MR-J2S-A manual. Change it at once on warning AL.9F.
Will I lose the absolute position when I change the battery?
On 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 control power off does, unless the backup procedure is followed. It also says to wait 15 minutes after switching off the main circuit power before replacing the battery.
What is the life of the smoothing capacitor?
The manuals give about 10 years of continuous operation at 40°C or less. Heat shortens it.
How often should servo motor bearings be changed?
There is no single figure we can verify from the amplifier manuals. Bearings are replaced on condition: unusual noise, vibration or heat found during inspection, or when the motor is repaired.
Can Star Automations help with these replacements?
Yes, through our repair service. Send the amplifier or servo motor with its label details and we can advise which parts to replace. We are an independent repairer, 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: .
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