Alarm guide · Yaskawa · Updated October 2026
Yaskawa A.C10 alarm: servo overrun detected
Yaskawa A.C10 means the servo overran: the motor moved out of control. The common causes are wrong motor wiring, an encoder fault or a bad parameter.
By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.
What the alarm means
The drive detected the motor running without proper control. Alarm numbers and wording can differ between series, so confirm with the manual for your unit.
Common causes
- Motor power wires in the wrong phase order
- Encoder fault or wrong encoder wiring
- Wrong motor or encoder parameter
- Brake or load issue
- Drive 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
After a new motor or cable, check wiring first. If it stays, test the motor and encoder.
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 Yaskawa servo motor repair, Yaskawa encoder repair and Yaskawa servo drive repair.
Questions
Does A.C10 appear after a motor replacement?
Often, when the wiring or the parameters do not match the new motor.
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.