Alarm guide · Mitsubishi · Updated October 2026
Mitsubishi AL.30 alarm: regenerative error
Mitsubishi AL.30 is a regenerative error: the regenerative energy from braking is more than the regeneration circuit can handle, or the regenerative parts have a fault.
By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.
What the alarm means
During deceleration the motor feeds energy back. The amplifier dumps it in a regenerative resistor. AL.30 means that circuit is overloaded, set wrongly, or damaged. Alarm numbers and wording can differ between series, so confirm with the manual for your unit.
Common causes
- Regenerative option too small for the load or wrong parameter setting
- Regenerative resistor open, loose or wrong value
- Very fast or frequent deceleration with high inertia
- High supply voltage
- Regenerative transistor fault in the amplifier
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.
- Note the exact alarm code and when it appears: at power-up, at start, or under load.
- Power off and turn the shaft by hand if safe: it should turn smoothly.
- Check the motor cable, encoder cable and connectors for damage and loose contacts.
- Check what changed recently: load, speed, settings, cables or a replaced part.
When to send it for repair
The motor is seldom at fault, but a vertical axis or a heavy load makes the motor feed back more energy. Check the mechanism and the regenerative setup first.
We test every motor on our Universal Servo Motor Repair Equipment, which reads and aligns the feedback and runs the motor under load without the original drive.
See Mitsubishi servo motor repair, Mitsubishi encoder repair and Mitsubishi servo drive repair.
Questions
Can I just raise the deceleration time?
Often yes, as a short-term step. It reduces regenerative energy. A permanent fix needs the right regenerative resistor and the correct parameter.
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.25 · AL.50 · AL.16 and AL.20
Brand names identify the units we repair. Star Automations is an independent multi-brand repair company and is not an OEM service centre.