What the Er.400 alarm means

DC bus voltage exceeded the upper threshold, usually from regenerative energy the braking resistor could not absorb or a high incoming supply. This is a routine repair in our workshop for INOVANCE IRCB500 / IRCB501 + SV660 servo systems, and we normally pin it down during the first site check.

Most common causes

  • Braking resistor open, disconnected, or undersized
  • Incoming AC voltage above rating
  • Deceleration too aggressive for the inertia
  • Voltage spikes from neighboring heavy loads
Field note: Begin with the first item in the list; it has a far higher on-machine occurrence rate than the others.

Step-by-step field fix

  1. Measure the braking resistor and inspect its wiring — start here
  2. Measure incoming supply voltage
  3. Soften deceleration ramps in the failing move
  4. Set the regenerative parameter to match the installed resistor
  5. Add line conditioning if plant power is spiky
Safety first: For INOVANCE er-400, 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 braking resistor and inspect its wiring — start here. Beyond that it is the DC bus and power stage work - leave it to a professional. On INOVANCE er-400: 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

INOVANCE er-400 belongs to the drive & power stage family. On INOVANCE er-400 the failing stage is Inovance servos (SV660N class), same family as the robot controller on the Inovance robot controllers (IRCB series and kin) - the fault sits on the energy chain: mains input, rectification, DC bus, braking resistor, inverter power devices and the drive board. We start reading INOVANCE er-400 at the pendant alarm screen (ER.xxx / 0x9xxx segments) and the servo panel Er code.

The chain involved in INOVANCE er-400 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

When INOVANCE er-400 fires, the site usually reports Braking resistor open, disconnected, or undersized 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 INOVANCE er-400 (Main Circuit Overvoltage); written by the Henghuan repair team, updated 2026-10-01.

Not sure? Don't force it — contact an engineer

Give us the alarm code, robot model and the action at the moment of the alarm, and our engineers can give you a quick read — phone or video remote diagnosis is free.

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Related Drive & Power Stage alarms

Er.201 — Hardware Overcurrent Er.210 — Motor Overload Er.410 — Main Circuit Undervoltage Er.610 — Drive Overload (I2t) Er.920 — Regenerative Overload
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 EFORT · JAKA · AUBO and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the INOVANCE er-400 alarm mean?

DC bus voltage exceeded the upper threshold, usually from regenerative energy the braking resistor could not absorb or a high incoming supply. This is a routine repair in our workshop for INOVANCE IRCB500 / IRCB501 + SV660 servo systems, and we normally pin it down during the first site check. INOVANCE er-400 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Braking resistor open, disconnected, or undersized".

QCan I clear a INOVANCE er-400 alarm myself?

Whether INOVANCE er-400 clears on its own depends on the outcome of "Measure the braking resistor and inspect its wiring — start here". Finish the flow with "Add line conditioning if plant power is spiky" to confirm INOVANCE er-400 - do not skip it. If that step is clean, the second most frequent cause on INOVANCE er-400 is "Incoming AC voltage above rating". If INOVANCE er-400 returns after two clears, or the checks point at Braking resistor open, disconnected, or undersized, stop the cell and call a professional robot repair engineer.

QFor drive/power alarms like INOVANCE er-400, what spares do you bring on site?

The commonest causes we see on INOVANCE er-400 are "Braking resistor open, disconnected, or undersized, Incoming AC voltage above rating, Deceleration too aggressive for the inertia", so we stock the van against those. For INOVANCE er-400 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 INOVANCE er-400, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what INOVANCE er-400 shows on the pendant alarm screen (ER.xxx / 0x9xxx segments) and the servo panel Er code and what the machine was doing - phone or video triage is free.

The content on INOVANCE er-400 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 INOVANCE documentation, or contact us to confirm. Henghuan is an independent service provider with no affiliation or endorsement by INOVANCE.