What the A.40 alarm means

The DC bus voltage in the drive exceeded the upper limit; typically caused by high incoming supply or un-dissipated regenerative energy. 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

  • Incoming AC supply above the rated range
  • Braking resistor open or disconnected
  • Voltage spikes from heavy equipment on the same feeder
  • Drive voltage detection circuit fault
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. Measure incoming three-phase voltage at the cabinet
  2. Verify the braking resistor and its wiring first — this is the usual culprit
  3. Check for voltage spikes when nearby welders or presses switch
  4. Reduce deceleration and retry
  5. Replace the drive only after supply and regeneration are proven healthy
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 Drive & Power Stage alarms

A.02 — Parameter Setting Error A.10 — Overcurrent A.30 — Regeneration Error / Regenerative Overload 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.40 alarm mean?

The DC bus voltage in the drive exceeded the upper limit; typically caused by high incoming supply or un-dissipated regenerative energy. In field practice it belongs to the drive & power stage family of faults.

QCan I clear a ESTUN A.40 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.