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. Our engineers run into this alarm every week on ESTUN ERC / ED3L controller + ESTUN servo controllers, and a single on-site inspection usually identifies the problem.

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: In our repair stats the first cause has the highest hit rate, so confirm it first before digging further.

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: For ESTUN a-02, 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. The self-serviceable action is Note the sub-code shown with A.02 to identify which parameter is invalid; anything past that falls under the DC bus and power stage and needs a certified engineer. On ESTUN a-02: 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-02 belongs to the drive & power stage family. On ESTUN a-02 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-02 at the pendant alarm list (A.xxx / E.xxx segments) and the servo panel display code.

The chain involved in ESTUN a-02 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

Bottom line up front: Parameters edited by hand and saved with out-of-range values is the first suspect for ESTUN a-02, but read it along the energy chain: Any link on this chain dropping voltage shows up at the end as a drive alarm, so order matters. We measure the mains first: more than 3% phase imbalance is enough to sag the bus under load, and plenty of bus over/under-voltage alarms are actually a grid problem wearing a robot costume. Mains fine, then the bus capacitors - bulged cases, weeping electrolyte or a lifted vent mean replacement; capacitance down 20% or more cannot hold the bus during braking. Last, the braking resistor: healthy values sit in the tens of ohms depending on rating, and an open or drifted resistor trips regenerative overvoltage directly.

Field notes on this page cover ESTUN a-02 (Parameter Setting Error); written by the Henghuan repair team, updated 2026-10-01.

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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
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-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. Our engineers run into this alarm every week on ESTUN ERC / ED3L controller + ESTUN servo controllers, and a single on-site inspection usually identifies the problem. ESTUN a-02 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Parameters edited by hand and saved with out-of-range values".

QCan I clear a ESTUN a-02 alarm myself?

Whether ESTUN a-02 clears on its own depends on the outcome of "Note the sub-code shown with A.02 to identify which parameter is invalid". Finish the flow with "Verify the motor model code matches the nameplate before servo-on" to confirm ESTUN a-02 - do not skip it. If that step is clean, the second most frequent cause on ESTUN a-02 is "Drive firmware updated but old parameter file reloaded". When ESTUN a-02 keeps coming back it is not a one-off trigger - especially if Verify the motor model code matches the nameplate before servo-on is where you get stuck. Do not keep producing through ESTUN a-02.

QFor drive/power alarms like ESTUN a-02, what spares do you bring on site?

The commonest causes we see on ESTUN a-02 are "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", so we stock the van against those. For ESTUN a-02 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-02, 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-02 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-02 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.