Mitsubishi Electric MELSERVO-J4 (MR-J4) alarm AL.25: Absolute position erased
Alarm AL.25 on a Mitsubishi MR-J4 servo amplifier is Absolute position erased: the absolute position data is faulty, or power was switched on for the first time in the absolute position detection system. After the cause is fixed, a home position return is required.
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When it happens
- At power-up, the first time in the absolute position detection system
- At power-up after the battery or CN4 was disconnected while control power was off
- At power-up after a long shutdown with a discharged battery
Reading the subset
| Subset | What it tells you |
|---|---|
| 25.1 | Servo motor encoder - Absolute position erased. |
| 25.2 | Scale measurement encoder - Absolute position erased. |
Likely causes and checks
1First power-up in the absolute position detection system
- Points to it
- New installation or absolute mode just enabled.
- Check
- Check that the battery is mounted correctly and perform home position return.
2Battery or CN4 disconnected while control power was off
- Points to it
- Battery or amplifier replaced with power off.
- Check
- Confirm what was disconnected; mount the battery correctly and perform home position return.
3Battery voltage low
- Points to it
- AL.9F (Battery warning) seen before.
- Check
- Measure the battery voltage with a tester; below 3 V DC, replace the battery and perform home position return.
4Non-recommended or faulty encoder or battery cable
- Points to it
- Battery good but alarm repeats.
- Check
- Check that a recommended encoder cable is used and test the battery and encoder cables for loose connections.
5Amplifier or encoder failure
- Points to it
- All of the above check good.
- Check
- Replace the amplifier and check repeatability, then the servo motor.
Telling it apart
- AL.9F (Battery warning) means the battery is low but position is still held; AL.92 means the battery cable is disconnected. AL.25 means the absolute data is gone.
- Never resume automatic operation after AL.25 without a home position return.
Evidence to collect
- Full alarm and detail number
- Battery type and measured voltage
- What was disconnected while power was off
- Alarm history showing AL.9F or AL.92 before the AL.25
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