What the E0028 alarm means

The motor supply voltage dropped below threshold; the amplifier cannot drive the motors reliably. This is one of the most common faults in our repair logs for the Nachi AW / FD series platform, and the first inspection typically locates the cause.

Most common causes

  • Incoming supply dip or phase loss
  • Loose main power connection
  • Failing power supply unit
  • High inrush from repeated starts
Field note: Field experience says the first cause is the most likely — verify it before moving on to the rest.

Step-by-step field fix

  1. Measure the incoming supply voltage under load
  2. Check main power connections and fuses
  3. Look for voltage dips when other equipment starts
  4. Check the power supply unit
  5. Reduce simultaneous axis starts if inrush is the cause
Safety first: For NACHI e0028, 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. On site you may not carry out the first step yourself: Measure the incoming supply voltage under load. Beyond that it is the DC bus and power stage work - leave it to a professional. On NACHI e0028: 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

NACHI e0028 belongs to the drive & power stage family. On NACHI e0028 the failing stage is servo amplifier modules in the cabinet, assigned per axis on the AX-series / FD-series controllers - the fault sits on the energy chain: mains input, rectification, DC bus, braking resistor, inverter power devices and the drive board. We start reading NACHI e0028 at the pendant error-code screen (E-series codes) with amplifier panel indicators.

The chain involved in NACHI e0028 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

When NACHI e0028 fires, the site usually reports Incoming supply dip or phase loss first, but the real cause is often cooling: More than half of power-stage alarms are not a dead device but a device cooked by failed cooling. A stopped cabinet fan, a packed filter mat or a dusted air duct keeps IGBT junction temperature high: intermittent over-temperature first, hard fault days later. On these alarms we open the power module and look for cracked thermal paste and felted dust in the duct, then measure phase-to-phase output and insulation to frame. Swapping the module without cleaning the duct just buys the same failure again.

Field notes on this page cover NACHI e0028 (Motor Power Voltage Drop); written by the Henghuan repair team, updated 2026-10-01.

Can't clear it yourself? Contact us for remote diagnosis

Just tell us the alarm code, the robot model and which program was running, and our engineers will help you narrow it down — phone and video remote diagnosis are both free.

Get a Free Remote Diagnosis See Repair Services

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

Related Drive & Power Stage alarms

E0032 — Overcurrent E0038 — Overload E0042 — Motor Temperature Rise Abnormal E0044 — Motor Power Overvoltage
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 Omron · ESTUN · INOVANCE and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the NACHI e0028 alarm mean?

The motor supply voltage dropped below threshold; the amplifier cannot drive the motors reliably. This is one of the most common faults in our repair logs for the Nachi AW / FD series platform, and the first inspection typically locates the cause. NACHI e0028 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Incoming supply dip or phase loss".

QCan I clear a NACHI e0028 alarm myself?

Whether NACHI e0028 clears on its own depends on the outcome of "Measure the incoming supply voltage under load". Finish the flow with "Reduce simultaneous axis starts if inrush is the cause" to confirm NACHI e0028 - do not skip it. If that step is clean, the second most frequent cause on NACHI e0028 is "Loose main power connection". After clearing NACHI e0028, watch it for one shift. A second trip means stop and let an engineer arrive with the right test gear for the DC bus and power stage.

QFor drive/power alarms like NACHI e0028, what spares do you bring on site?

The commonest causes we see on NACHI e0028 are "Incoming supply dip or phase loss, Loose main power connection, Failing power supply unit", so we stock the van against those. For NACHI e0028 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 NACHI e0028, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what NACHI e0028 shows on the pendant error-code screen (E-series codes) with amplifier panel indicators and what the machine was doing - phone or video triage is free.

The content on NACHI e0028 was written by Henghuan Robotics service engineers from hands-on repair experience. Alarm descriptions are our own reference summary and may differ by controller or software version — defer to Nachi documentation, or contact us to confirm. Henghuan is an independent service provider with no affiliation or endorsement by Nachi.