Alarm guide · Yaskawa · Updated October 2026
Yaskawa A.300 alarm: regeneration error
Yaskawa A.300 is a regeneration error on Sigma drives. The regenerative circuit or resistor is the usual suspect: a failed or missing regeneration resistor, a wrong setting, or a fault in the drive.
By Suresh Sankaran, founder of Star Automations, servo motor repair since 1998.
What the alarm means
The drive found a fault in the regeneration circuit, which burns off energy when the motor decelerates a heavy load. Alarm numbers differ between Sigma series, so confirm with the manual for your drive.
Common causes
- Open or damaged regeneration resistor, or loose wiring to it
- Wrong regeneration resistor setting
- Regeneration transistor or related circuit failure in the drive
- Load too heavy or deceleration too fast for the resistor
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 let the DC bus discharge before touching terminals.
- Check the regeneration resistor wiring and the resistor continuity.
- Check the parameter for the regeneration resistor against what is fitted.
- Check whether the deceleration time or load changed recently.
When to send it for repair
Send the drive when the resistor and settings are correct and the alarm stays. The regeneration circuit is repaired at component level and the drive is tested with a motor under load.
See Yaskawa servo motor repair, Yaskawa encoder repair and Yaskawa servo drive repair.
Questions
Is A.300 a motor fault?
Not usually. It is a drive and regeneration circuit alarm, so check the resistor and settings first.
Can I use the drive without the resistor?
Follow the drive manual. Running a heavy load without the correct resistor can damage the drive.
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.