What the 9720 alarm means

When controller power was applied, an axis was detected moving too fast (e.g. The robot was falling or being pushed while unpowered); the encoder sees motion at startup and faults. We fix this Epson RC90 / RC700 (EPSON RC+) fault almost daily, and one round of on-site checks usually confirms what is going on.

Most common causes

  • Axis moved while unpowered (brake released manually, gravity drop)
  • Robot pushed while powered off
  • Encoder glitch at power-on
Field note: We have tallied real cases: the first cause tops the list, so start your diagnosis there.

Step-by-step field fix

  1. Stop the robot and reboot the controller
  2. Inspect whether any axis physically moved while unpowered
  3. If a gravity axis dropped, support it, release the brake properly and re-home
  4. Check the brake on the affected axis
  5. If nothing moved, check encoder wiring and reboot again
Safety first: For EPSON 9720, the risk on this family is not injury but data: lose the program, parameters and calibration data and weeks of teaching work start over. The self-serviceable action is Stop the robot and reboot the controller; anything past that falls under program and calibration data and needs a certified engineer.

How we diagnose system alarms on site

EPSON 9720 belongs to the system & program family. On EPSON 9720 the failing stage is SPEL+ / EPSON RC+ environment (RC700-A / RC90-B and the RC series) on the RC700-A / RC90-B and the RC series - the software layer: corrupted program or parameter files, boot failures, version mismatch, memory and storage media. We start reading EPSON 9720 at the EPSON RC+ error list and controller front-panel indicators; codes segment as 4xxx / 5xxx / 9xxx.

The chain involved in EPSON 9720 runs: storage media (CF / flash / disk) -> system software and firmware -> parameters and calibration data -> user programs -> runtime.

EPSON 9720 is a system-family alarm, and our iron rule is: On system alarms we have an iron rule: however urgent the customer is, we take a complete backup first - programs, parameters, calibration data, tool and work-object frames, all of it. The reason is arithmetic: losing the live state here usually means weeks of teaching done again, which costs far more than a few hours of downtime. Only after the backup do we decide restart, restore or reinstall. If the storage media is already throwing errors we pull the data read-only first.

Field notes on this page cover EPSON 9720 (Speed Too High at Controller Power-On); 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. EPSON 9720 is a diagnosis our engineers do daily, and phone/video remote diagnosis is free.

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Related System & Program alarms

4100 — Communication Error in Motion Control Module 4105 — Emergency Connector Connection Failure 4150 — Redundant Input Signal Failure of Emergency Stop 4152 — Relay Welding Error of Main Circuit 4154 — Regeneration Resistor Overtemperature 5040 — Motor Torque Output Failure — High Power State
Same family: this code belongs to the System & program alarms family - the page collects all System & program-family codes we have handled, with the common inspection order and spares.
Other brands: we also keep field-fix libraries for Nachi · Omron · ESTUN and more — see the complete alarm code hub.

Frequently asked questions

QWhat does the EPSON 9720 alarm mean?

When controller power was applied, an axis was detected moving too fast (e.g. The robot was falling or being pushed while unpowered); the encoder sees motion at startup and faults. We fix this Epson RC90 / RC700 (EPSON RC+) fault almost daily, and one round of on-site checks usually confirms what is going on. EPSON 9720 sits in the system & program family; on our work orders the highest-frequency trigger for this code is "Axis moved while unpowered (brake released manually, gravity drop)".

QCan I clear a EPSON 9720 alarm myself?

Whether EPSON 9720 clears on its own depends on the outcome of "Stop the robot and reboot the controller". Finish the flow with "If nothing moved, check encoder wiring and reboot again" to confirm EPSON 9720 - do not skip it. If that step is clean, the second most frequent cause on EPSON 9720 is "Robot pushed while powered off". Do not chase takt through a repeating EPSON 9720. Left alone, system & program faults tend to graduate from repairable to must-replace.

QWhen you handle EPSON 9720, will my programs and frames get lost?

The commonest causes we see on EPSON 9720 are "Axis moved while unpowered (brake released manually, gravity drop), Robot pushed while powered off, Encoder glitch at power-on", so we stock the van against those. For EPSON 9720 specifically, we carry recovery media and common storage media, but on this family the backup matters more than the spare. For EPSON 9720, on system alarms the first move is backup; we can walk the customer through preserving data remotely before anything else. Before we roll, tell us what EPSON 9720 shows on the EPSON RC+ error list and controller front-panel indicators; codes segment as 4xxx / 5xxx / 9xxx and what the machine was doing - phone or video triage is free.

The notes on EPSON 9720 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 Epson documentation or contact us with questions. Henghuan is an independent service provider, not affiliated with or endorsed by Epson.