What the SRVO-021 alarm means

The servo amplifier for the specified axis did not report ready when servo power was switched on, so the controller cut servo power. This is one of the faults our repair team handles most often — the cause is usually identifiable within the first on-site inspection.

Most common causes

  • Servo amplifier fault for that axis
  • E-stop/safety circuit not closed
  • Power cable or signal cable between controller and amplifier loose
  • Axis control card failure
Field note: the first item on this list is what we find most often on real machines. Check it before you go deeper.

Step-by-step field fix

  1. Check the 7-segment LED on the servo amplifier for its own alarm code
  2. Verify E-stop chain is reset and chain circuit is healthy
  3. Inspect power and signal connectors on the amplifier
  4. Swap the amplifier with a known-good unit to isolate amp vs. wiring
Safety first: never bypass safety circuits or force contactors closed. If the alarm involves E-stop chains or servo power, and you are not a trained robot technician, contact a professional — wrong moves here can cost you a robot or an injury.

Still stuck? Get an engineer on the phone — right now

Tell us the alarm code, the robot model and what was happening when the alarm came up. Our engineers run these diagnostics every day, and remote diagnosis by phone or video call is free.

Get a Free Remote Diagnosis See Repair Services

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

Related Servo & Drive alarms

SRVO-023 — Stop Error Excess (Group / Axis) SRVO-024 — Move Error Excess (Group / Axis) SRVO-043 — DCAL Alarm - Discharge Alarm SRVO-044 — HVAL Alarm - High Voltage SRVO-045 — HCAL Alarm - High Current SRVO-046 — OVC Alarm - Overcurrent (Average)
Other brands: see our KUKA, ABB, Yaskawa and Universal Robots field-fix libraries — or the full 10-brand hub.

Frequently asked questions

QWhat does the FANUC SRVO-021 alarm mean?

The servo amplifier for the specified axis did not report ready when servo power was switched on, so the controller cut servo power. In field practice it belongs to the servo & drive family of faults.

QCan I clear a FANUC SRVO-021 alarm myself?

Sometimes. Follow the step-by-step checks on this page — start with the first cause listed, which is what we find most often in the field. If the alarm returns after two attempts, or the fault involves power/safety circuits, stop and call a qualified robot service engineer.

QHow fast can a Henghuan engineer help?

On-site response in the Pearl River Delta within 30 minutes to 3 hours, across mainland China in 1–3 business days, and worldwide within 2–5 business days. Remote diagnosis by phone/WhatsApp/video is available immediately.

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 version — when in doubt, check your FANUC documentation or contact us. Henghuan is an independent service provider, not affiliated with or endorsed by FANUC.