Alarm guide · Mitsubishi · Updated October 2026
Mitsubishi AL.50 alarm: overload 1
Mitsubishi AL.50 is an overload alarm: the drive or motor carried more current than allowed for too long. The usual causes are a heavy or jammed mechanism, a brake that stayed on, wrong settings, or a failing motor.
By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.
What the alarm means
The drive tripped on thermal overload protection after running above the rated load for too long. Alarm numbers differ between MELSERVO series, so confirm with the manual for your drive.
Common causes
- Mechanical jam, heavy load or high friction
- Brake not released
- Wrong gain or acceleration settings
- Motor winding or bearing fault
- Motor wiring fault
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.
- Power off and turn the shaft by hand if safe: it should turn smoothly.
- Check that the brake releases when powered.
- Check the motor cable and connectors.
- Check recent changes to load, speed or settings.
When to send it for repair
Send the motor when the shaft is stiff, noisy or hot, or the alarm stays with a free mechanism. Send the drive if the motor tests good.
See Mitsubishi servo motor repair, Mitsubishi encoder repair and Mitsubishi servo drive repair.
Questions
What is the difference between AL.50 and AL.51?
AL.50 is overload 1 (a long-time load). AL.51 is overload 2 (a short, very high load). Both point to load, brake, motor or setting problems.
Can a reset clear it?
Only until the same load returns. Find why the load was high.
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.