What the A.02 alarm means

One or more servo parameters stored in the ESTUN drive are outside the valid range or inconsistent with each other; the drive refuses servo-on until the parameters are corrected. This is one of the faults our repair team handles on ESTUN ERC / ED3L controller + ESTUN servo systems — the cause is usually identifiable within the first on-site inspection.

Most common causes

  • Parameters edited by hand and saved with out-of-range values
  • Drive firmware updated but old parameter file reloaded
  • Parameter corruption after a power dip during write
  • Wrong motor model code entered for the connected motor
Field note: the first item on this list is what we find most often on real machines. Check it before you go deeper.

Step-by-step field fix

  1. Note the sub-code shown with A.02 to identify which parameter is invalid
  2. Compare the parameter against the ESTUN parameter manual default table
  3. Re-enter the correct value, save, and power-cycle the drive
  4. If many parameters are invalid, restore from a known-good backup file
  5. Verify the motor model code matches the nameplate before servo-on
Safety first: never bypass safety circuits or force contactors closed. If the alarm involves E-stop chains, brakes or drive power, and you are not a trained robot technician, contact a professional — wrong moves here can cost you a robot or an injury.

Still stuck? Get an engineer on the phone — right now

Tell us the alarm code, the robot model and what was happening when the alarm came up. Our engineers run these diagnostics every day, and remote diagnosis by phone or video call is free.

Get a Free Remote Diagnosis See Repair Services

Hotline: +86-20-39029800 · WhatsApp: +86-188-1886-2860

Related Drive & Power Stage alarms

A.10 — Overcurrent A.30 — Regeneration Error / Regenerative Overload A.40 — Main Circuit Overvoltage A.41 — Main Circuit Undervoltage A.71 — Overload — Instantaneous High Load A.72 — Overload — Continuous Over-torque
Other brands: we also keep field-fix libraries for INOVANCE · EFORT · JAKA and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the ESTUN A.02 alarm mean?

One or more servo parameters stored in the ESTUN drive are outside the valid range or inconsistent with each other; the drive refuses servo-on until the parameters are corrected. In field practice it belongs to the drive & power stage family of faults.

QCan I clear a ESTUN A.02 alarm myself?

Sometimes. Work through the step-by-step checks on this page — the first listed cause is what we find most often in the field. If the alarm returns after two attempts, or the fault involves power, brakes or safety circuits, stop and call a qualified robot service engineer.

QHow fast can a Henghuan engineer help?

On-site response in the Pearl River Delta within 30 minutes to 3 hours, across mainland China in 1-3 business days, and worldwide within 2-5 business days. Remote diagnosis by phone/WhatsApp/video is available immediately.

Written by the Henghuan Robotics repair team from field service experience. Alarm descriptions are our own summary for troubleshooting reference and may vary by controller and software version — when in doubt, check your ESTUN documentation or contact us. Henghuan is an independent service provider, not affiliated with or endorsed by ESTUN.