What the A.720 alarm means

The motor ran continuously above rated torque; unlike A.710 this builds up slowly and usually points at a systemic mechanical or setup problem rather than a single collision. This is a routine repair in our workshop for Yaskawa DX100 / DX200 / YRC1000 systems, and we normally pin it down during the first site check.

Most common causes

  • Payload setting higher or lower than the real tool weight
  • Unbalanced axis (balancer pressure wrong on J2/J3)
  • Worn reducer creating drag
  • Cabinet ambient temperature too high
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. Confirm the payload/inertia parameters match the actual end effector
  2. Check gas balancer pressure where applicable
  3. Listen for reducer noise and check axis backdrivability with power off
  4. Lower ambient temperature or improve cabinet ventilation
  5. If current remains high with no load, test the motor and SERVOPACK
Safety first: For YASKAWA a-720, 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 Confirm the payload/inertia parameters match the actual end effector; anything past that falls under the DC bus and power stage and needs a certified engineer. On YASKAWA a-720: 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

YASKAWA a-720 belongs to the drive & power stage family. On YASKAWA a-720 the failing stage is Yaskawa Sigma-series servo drives (servo packs) assigned per axis in the cabinet on the DX100 / DX200 / YRC1000 / YRC1000micro - the fault sits on the energy chain: mains input, rectification, DC bus, braking resistor, inverter power devices and the drive board. We start reading YASKAWA a-720 at the pendant alarm list (A / E / 4xxx segments) together with the servo drive's digit display.

The chain involved in YASKAWA a-720 runs: three-phase mains -> rectifier -> DC bus (bus capacitors) -> brake chopper / braking resistor -> inverter (IGBT) -> motor.

Bottom line up front: Payload setting higher or lower than the real tool weight is the first suspect for YASKAWA a-720, 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 YASKAWA a-720 (Overload — Low Load (Continuous Over-torque)); written by the Henghuan repair team, updated 2026-10-01.

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Related Drive & Power Stage alarms

A.100 — Overcurrent or Heat Sink Overheated (SERVOPACK) A.320 — Regenerative Overload A.400 — Overvoltage — Main Circuit DC Voltage Too High A.410 — Undervoltage — Main Circuit DC Voltage Too Low A.710 — Overload — High Load (Stall-level Torque) A.7A0 — Heat Sink Overheated (>100 degC)
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 Universal Robots · Kawasaki · Staubli and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the YASKAWA a-720 alarm mean?

The motor ran continuously above rated torque; unlike A.710 this builds up slowly and usually points at a systemic mechanical or setup problem rather than a single collision. This is a routine repair in our workshop for Yaskawa DX100 / DX200 / YRC1000 systems, and we normally pin it down during the first site check. YASKAWA a-720 sits in the drive & power stage family; on our work orders the highest-frequency trigger for this code is "Payload setting higher or lower than the real tool weight".

QCan I clear a YASKAWA a-720 alarm myself?

Whether YASKAWA a-720 clears on its own depends on the outcome of "Confirm the payload/inertia parameters match the actual end effector". Finish the flow with "If current remains high with no load, test the motor and SERVOPACK" to confirm YASKAWA a-720 - do not skip it. If that step is clean, the second most frequent cause on YASKAWA a-720 is "Unbalanced axis (balancer pressure wrong on J2/J3)". If YASKAWA a-720 returns after two clears, or the checks point at Payload setting higher or lower than the real tool weight, stop the cell and call a professional robot repair engineer.

QFor drive/power alarms like YASKAWA a-720, what spares do you bring on site?

The commonest causes we see on YASKAWA a-720 are "Payload setting higher or lower than the real tool weight, Unbalanced axis (balancer pressure wrong on J2/J3), Worn reducer creating drag", so we stock the van against those. For YASKAWA a-720 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 YASKAWA a-720, drive alarms usually stop the whole line, so they sit at the front of our dispatch queue. Before we roll, tell us what YASKAWA a-720 shows on the pendant alarm list (A / E / 4xxx segments) together with the servo drive's digit display and what the machine was doing - phone or video triage is free.

This page on YASKAWA a-720 was compiled from actual repair records of the Henghuan Robotics repair team. Alarm notes are our own summary for troubleshooting reference only and may vary with controller and software version — please consult Yaskawa documentation or contact us if in doubt. Henghuan is an independent service provider, not affiliated with or endorsed by Yaskawa.