What the 34251 alarm means

One phase of the incoming three-phase supply to the drive is missing — the rectifier cannot build a proper DC link. This fault ranks high in our ABB IRC5 / OmniCore (RobotWare) service records, and the first site inspection usually finds the source.

Most common causes

  • Blown input fuse on one phase
  • Broken supply cable or terminal
  • Upstream breaker or phase-loss relay tripped
  • Utility supply fault
Field note: The first cause shows up most on real machines, so verify it before you go further.

Step-by-step field fix

  1. Measure all three input phases at the cabinet
  2. Replace blown fuses and find why they blew
  3. Tighten input terminals
  4. Check upstream breakers and the facility supply
Safety first: For ABB 34251, 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 all three input phases at the cabinet; the DC bus and power stage handling is not a DIY job. On ABB 34251: 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

ABB 34251 belongs to the drive & power stage family. On ABB 34251 the failing stage is DSQC drive modules (DSQC 600 generation; OmniCore drive units) on the IRC5 / OmniCore - the fault sits on the energy chain: mains input, rectification, DC bus, braking resistor, inverter power devices and the drive board. We start reading ABB 34251 at the FlexPendant event log and system diagnostics, with the cabinet status LEDs.

The chain involved in ABB 34251 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

Blown input fuse on one phase is common on ABB 34251, 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 ABB 34251 (Missing Phase of Input Power); written by the Henghuan repair team, updated 2026-10-01.

If you can't fix it, reach our engineers directly

Tell us these three: alarm code, robot model, and the operating condition at the alarm. ABB 34251 is a diagnosis our engineers do daily, and phone/video remote diagnosis is free.

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Related Drive & Power Stage alarms

34316 — Motor Current Error 34200 — Communication with All Drive Units Interrupted 34400 — DC Link Voltage Too High
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 Yaskawa · Universal Robots · Kawasaki and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the ABB 34251 alarm mean?

One phase of the incoming three-phase supply to the drive is missing — the rectifier cannot build a proper DC link. This fault ranks high in our ABB IRC5 / OmniCore (RobotWare) service records, and the first site inspection usually finds the source. ABB 34251 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Blown input fuse on one phase".

QCan I clear a ABB 34251 alarm myself?

Whether ABB 34251 clears on its own depends on the outcome of "Measure all three input phases at the cabinet". Finish the flow with "Check upstream breakers and the facility supply" to confirm ABB 34251 - do not skip it. If that step is clean, the second most frequent cause on ABB 34251 is "Broken supply cable or terminal". If ABB 34251 returns after two clears, or the checks point at Blown input fuse on one phase, stop the cell and call a professional robot repair engineer.

QFor drive/power alarms like ABB 34251, what spares do you bring on site?

The commonest causes we see on ABB 34251 are "Blown input fuse on one phase, Broken supply cable or terminal, Upstream breaker or phase-loss relay tripped", so we stock the van against those. For ABB 34251 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 ABB 34251, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what ABB 34251 shows on the FlexPendant event log and system diagnostics, with the cabinet status LEDs and what the machine was doing - phone or video triage is free.

The notes on ABB 34251 were summarized by the Henghuan Robotics repair team from on-site service. The alarm interpretation is our empirical summary for troubleshooting reference and may vary by controller and software version — please check ABB documentation or contact us with questions. Henghuan is an independent service provider, not affiliated with or endorsed by ABB.