What the A# alarm means

The servo amplifier for the indicated joint reports a fault; that joint cannot be driven. Our engineers run into this alarm every week on Omron SmartController (ACE / Viper / Cobra) controllers, and a single on-site inspection usually identifies the problem.

Most common causes

  • Amplifier overcurrent or overtemperature
  • Motor winding or cable fault loading the amplifier
  • Failed amplifier module
  • DC bus problem shared between amplifiers
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 joint number from the status panel
  2. Check motor cable and motor resistance for that joint
  3. Power-cycle once and retry
  4. Swap-test the amplifier module if possible
  5. Replace the amplifier and verify with a low-speed jog
Safety first: For OMRON a, 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 joint number from the status panel; anything past that falls under the DC bus and power stage and needs a certified engineer. On OMRON a: 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

OMRON a belongs to the drive & power stage family. On OMRON a the failing stage is integrated drive units (amplifier and supply in one housing) on the OMRON robot controllers (including SCARA and cobot companions) - the fault sits on the energy chain: mains input, rectification, DC bus, braking resistor, inverter power devices and the drive board. We start reading OMRON a at controller status indicators and the software error list (letter prefixes RC / SW / V / M / D / A / E).

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

Amplifier overcurrent or overtemperature is common on OMRON a, 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 OMRON a (Amplifier Fault (Joint N)); written by the Henghuan repair team, updated 2026-10-01.

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Related Drive & Power Stage alarms

D# (-1021) — Duty Cycle Exceeded (Joint N) 24 — 24V Supply Fault h# — High Temperature — Amplifier (Joint N) hV — High Voltage Bus Fault
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 ESTUN · INOVANCE · EFORT and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the OMRON a alarm mean?

The servo amplifier for the indicated joint reports a fault; that joint cannot be driven. Our engineers run into this alarm every week on Omron SmartController (ACE / Viper / Cobra) controllers, and a single on-site inspection usually identifies the problem. OMRON a sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Amplifier overcurrent or overtemperature".

QCan I clear a OMRON a alarm myself?

Whether OMRON a clears on its own depends on the outcome of "Note the joint number from the status panel". Finish the flow with "Replace the amplifier and verify with a low-speed jog" to confirm OMRON a - do not skip it. If that step is clean, the second most frequent cause on OMRON a is "Motor winding or cable fault loading the amplifier". If OMRON a returns after two clears, or the checks point at Amplifier overcurrent or overtemperature, stop the cell and call a professional robot repair engineer.

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

The commonest causes we see on OMRON a are "Amplifier overcurrent or overtemperature, Motor winding or cable fault loading the amplifier, Failed amplifier module", so we stock the van against those. For OMRON a 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 OMRON a, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what OMRON a shows on controller status indicators and the software error list (letter prefixes RC / SW / V / M / D / A / E) and what the machine was doing - phone or video triage is free.

This page on OMRON a 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 Omron documentation or contact us. Henghuan is an independent service provider, not affiliated with or endorsed by Omron.