Alarm guide · Mitsubishi · Updated October 2026
Mitsubishi AL.45 alarm: main circuit device overheat
Mitsubishi AL.45 means the power devices in the servo amplifier overheated. Check cooling, the cabinet temperature and the load.
By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.
What the alarm means
The temperature sensor on the amplifier power stage crossed its limit. Alarm numbers and wording can differ between series, so confirm with the manual for your unit.
Common causes
- Blocked vents, dirty heat sink or failed fan
- High cabinet temperature
- Load above the amplifier rating
- Very frequent acceleration and deceleration
- Power device or sensor 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.
- 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
This one is mainly the amplifier and its cooling. A motor with a partial short can load the amplifier more, so test the motor if it returns.
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 clean the fan and restart?
Yes, after power off and discharge. If the alarm returns with clean cooling, send the amplifier for repair.
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.