Alarm guide · Mitsubishi · Updated October 2026
Mitsubishi AL.25 alarm: absolute position erased
Mitsubishi AL.25 means the absolute position data was lost. It usually follows a flat or removed battery, a disconnected encoder cable, or an encoder fault. The axis has to be homed again after the cause is fixed.
By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.
What the alarm means
The drive lost the absolute position stored for the encoder. This happens when the backup power to the encoder was interrupted. Alarm numbers differ between MELSERVO series, so confirm with the manual for your drive.
Common causes
- Flat, missing or loose backup battery
- Encoder cable disconnected while the drive power was off
- Encoder fault
- Cable or connector damage
Safe first checks
General guidance only. Follow the drive manual and your site's electrical safety rules. Power off, and let the DC bus discharge, before touching connectors.
- Check the battery voltage and the battery connection.
- Reseat the encoder cable at both ends with power off.
- Inspect the encoder cable for damage.
- After the fix, home the axis again as the machine manual describes.
When to send it for repair
Send the motor when AL.25 returns with a good battery and cable, because the encoder may be failing. See also our absolute encoder battery guide.
See Mitsubishi servo motor repair, Mitsubishi encoder repair and Mitsubishi servo drive repair.
Questions
Is AL.25 always the battery?
It is the most common cause, but if it returns with a new battery, test the cable and the encoder.
Will I lose my machine zero?
Yes, the axis must be homed again. Follow your machine manual.
How long does repair take?
Emergency repair is done the same day where the fault and parts allow, urgent in 3 working days and standard in 7 working days, counted from when the unit reaches our bench and the quote is approved. Every unit returns with a printed test report.
Can I get an exchange unit?
If we hold a matching unit, Servo Swap ships a tested exchange unit while yours is repaired. Mark "line down" on the request form and add the part number.
Related: AL.16 and AL.20 · AL.25 · AL.32 · AL.50
Brand names identify the units we repair. Star Automations is an independent multi-brand repair company and is not an OEM service centre.