What the A.81 alarm means

The absolute encoder lost both main power and battery backup, so multi-turn position data is gone; the axis must be re-zeroed before the robot can run. 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

  • Encoder backup battery dead
  • Battery connector loose or corroded
  • Motor cable disconnected while controller power was off
  • Absolute encoder faulty
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. Fit a fresh encoder battery
  2. Clean and reseat the battery connector
  3. Run the zeroing / absolute setup procedure on the affected axis
  4. Jog to the mechanical scribe marks and verify the zero values
  5. Replace the encoder (motor) if the alarm returns after setup
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.

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

Related Encoder & Position alarms

A.83 — Encoder Battery Voltage Low A.90 — Encoder Communication Error
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.81 alarm mean?

The absolute encoder lost both main power and battery backup, so multi-turn position data is gone; the axis must be re-zeroed before the robot can run. In field practice it belongs to the encoder & position family of faults.

QCan I clear a ESTUN A.81 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.