Mitsubishi MR-J4 AL.25: Absolute position erased after battery replacement, what to check?
I replaced the battery on my Mitsubishi MR-J4 servo amplifier while the control power was off, and now I'm getting an AL.25 fault. What should I check first to clear this alarm?
The AL.25 alarm on a Mitsubishi MR-J4 servo amplifier indicates that the absolute position data has been erased or is faulty. This can occur after initial power-up in an absolute position detection system, or if the battery or CN4 connector was disconnected while control power was off. A home position return is always required after resolving the cause of this alarm.
Likely causes and checks
1Battery or CN4 disconnected while control power was off
- Points to it
- Disconnecting the battery or CN4 connector while the control power is off can lead to the loss of absolute position data, triggering the AL.25 alarm upon power-up.
- Check
- Confirm what was disconnected (battery or CN4). Ensure the battery is mounted correctly and then perform a home position return.
2First power-up in the absolute position detection system
- Points to it
- If this is a new installation or the absolute mode has just been enabled for the first time, the system will not have absolute position data stored, leading to AL.25.
- Check
- Check that the battery is mounted correctly and perform a home position return.
3Battery voltage low
- Points to it
- A low battery voltage can cause the absolute position data to be lost, especially if the system was shut down for an extended period. This is often preceded by an AL.9F (Battery warning) alarm.
- Check
- Measure the battery voltage with a tester. If it is below 3 V DC, replace the battery and perform a home position return.
4Non-recommended or faulty encoder or battery cable
- Points to it
- Even if the battery itself is good, an incorrect or damaged encoder or battery cable can prevent the absolute position data from being maintained or read correctly.
- Check
- Check that a recommended encoder cable is used and test both the battery and encoder cables for loose connections.
Next check: After confirming the battery is correctly mounted and addressing any disconnections, perform a home position return. Never resume automatic operation after an AL.25 without performing a home position return.
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