What the A.41 alarm means

The DC bus voltage dropped below the lower limit; the drive cannot hold torque and shuts the axis down. We fix this ESTUN ERC / ED3L controller + ESTUN servo fault almost daily, and one round of on-site checks usually confirms what is going on.

Most common causes

  • Incoming AC voltage low or a momentary dip
  • Blown input fuse or open phase
  • Loose main-circuit terminal connections
  • Inrush resistor damaged by frequent power cycling
Field note: We have tallied real cases: the first cause tops the list, so start your diagnosis there.

Step-by-step field fix

  1. Measure supply voltage under load, not just at idle
  2. Check input fuses and all three phases
  3. Tighten main-circuit terminals and inspect for heat discoloration
  4. Limit power ON/OFF cycling frequency
  5. If supply is stable, suspect the inrush circuit or the drive itself
Safety first: For ESTUN a-41, this alarm family involves the DC bus, which sits at several hundred volts and stays charged for minutes after power-off - touching terminals is a shock hazard. What you can check yourself first is Measure supply voltage under load, not just at idle; the DC bus and power stage handling is not a DIY job. On ESTUN a-41: checking incoming voltage at the disconnect and looking at breakers and fuses is fine to do yourself; opening the cabinet to touch bus terminals or pulling power modules needs a qualified electrician.

How we diagnose drive alarms on site

ESTUN a-41 belongs to the drive & power stage family. On ESTUN a-41 the failing stage is matched servo drives (in-house / Inovance-class servos) on the ESTUN robot controllers (motion-control-platform based) - the fault sits on the energy chain: mains input, rectification, DC bus, braking resistor, inverter power devices and the drive board. We start reading ESTUN a-41 at the pendant alarm list (A.xxx / E.xxx segments) and the servo panel display code.

The chain involved in ESTUN a-41 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

Incoming AC voltage low or a momentary dip is common on ESTUN a-41, but look at the duty cycle: Cells with high-inertia loads or frequent start-stop cycles return far more regenerative energy than a plain transfer cell, and the braking resistor lives in a hot cycle that shortens its life. When we suspect this family we ask what changed: if the takt was raised recently or a heavier fixture went on, the alarm cluster usually lines up with that process change. Replacing the resistor alone will not fix it - the chopper rating and resistor wattage have to be re-checked against the new duty.

Field notes on this page cover ESTUN a-41 (Main Circuit Undervoltage); written by the Henghuan repair team, updated 2026-10-01.

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Related Drive & Power Stage alarms

A.02 — Parameter Setting Error A.10 — Overcurrent A.30 — Regeneration Error / Regenerative Overload A.40 — Main Circuit Overvoltage A.71 — Overload — Instantaneous High Load A.72 — Overload — Continuous Over-torque
Same family: this code belongs to the Drive & power stage alarms family - the page collects all Drive & power stage-family codes we have handled, with the common inspection order and spares.
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-41 alarm mean?

The DC bus voltage dropped below the lower limit; the drive cannot hold torque and shuts the axis down. We fix this ESTUN ERC / ED3L controller + ESTUN servo fault almost daily, and one round of on-site checks usually confirms what is going on. ESTUN a-41 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Incoming AC voltage low or a momentary dip".

QCan I clear a ESTUN a-41 alarm myself?

Whether ESTUN a-41 clears on its own depends on the outcome of "Measure supply voltage under load, not just at idle". Finish the flow with "If supply is stable, suspect the inrush circuit or the drive itself" to confirm ESTUN a-41 - do not skip it. If that step is clean, the second most frequent cause on ESTUN a-41 is "Blown input fuse or open phase". If ESTUN a-41 returns after two clears, or the checks point at Incoming AC voltage low or a momentary dip, stop the cell and call a professional robot repair engineer.

QFor drive/power alarms like ESTUN a-41, what spares do you bring on site?

The commonest causes we see on ESTUN a-41 are "Incoming AC voltage low or a momentary dip, Blown input fuse or open phase, Loose main-circuit terminal connections", so we stock the van against those. For ESTUN a-41 specifically, we stock the van along the energy chain: braking resistors, bus capacitors, input fuses, drive-board supply parts and the common power modules for the brand. For ESTUN a-41, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what ESTUN a-41 shows on the pendant alarm list (A.xxx / E.xxx segments) and the servo panel display code and what the machine was doing - phone or video triage is free.

This page on ESTUN a-41 was 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.