FANUC Robot Repair: SRVO-021 Event Log Triage

FANUC robot repair for SRVO-021 SRDY OFF should begin with the event log, Group and Axis information, controller identity, and HRDY/SRDY status. Within the verified R-30iB Mate and R-30iB Mate Plus scope, this alarm means HRDY is ON while SRDY remains OFF, no other alarm explains the state, and the servo amplifier magnetic contactor did not turn on as commanded. This symptom may involve connections, an instantaneous power interruption, the emergency-stop unit, or the servo amplifier, but it does not independently prove amplifier damage.

Symptoms and Applicable Scope

This article addresses SRVO-021 SRDY OFF on FANUC R-30iB Mate and R-30iB Mate Plus controllers covered by maintenance manual B-83525EN/07. The diagnostic objective is to preserve alarm chronology and determine why the servo-ready command was not completed.

The cited definition and sequence should not automatically be applied to other FANUC controller generations. Connector locations, circuit arrangements and service procedures depend on the installed controller, robot, auxiliary-axis configuration and manual revision. Use the maintenance information matching the controller identification plate and system configuration.

Information to Record First

Do not clear the alarm history before recording the event. An earlier alarm may explain why SRDY remained OFF, changing the appropriate diagnostic branch. Capture the following information without inserting assumptions:

Complete alarm code and full text:
Date and exact time:
Faulted axis:
Robot position/posture:
Program step or motion:
Actual speed and load condition:
Reset result:
Time until recurrence:
Related power, communication or feedback alarms:

For SRVO-021, also record the displayed Group and Axis. Identify the robot model, controller model, installed options and servo-amplifier label. Note whether the alarm appeared during startup, motor enable, production, recovery from an emergency stop, or another clearly identified operating stage.

Safety and Preparation

Place the robot in a safe state according to the applicable FANUC documentation and site lockout procedures before inspecting cabinet connections or components. Stored electrical energy and unexpected robot motion can create serious hazards. Cabinet access, electrical inspection and controlled restart should be performed only by suitably competent personnel.

Do not repeatedly reset or cycle power merely to reproduce an intermittent event. Preserve controller records before taking actions that could overwrite useful history. Do not disconnect or reconnect internal wiring while energized unless an applicable manufacturer procedure expressly requires a defined test by qualified personnel.

FANUC Robot Repair Diagnostic Sequence

First, record the complete code, Group and Axis. Confirm that the displayed event is SRVO-021 SRDY OFF rather than a shortened maintenance note. If multiple groups or auxiliary axes are installed, identify exactly which group generated the alarm before selecting drawings or inspecting hardware.

Second, review the event history for an earlier alarm. If an earlier event explains the servo-ready state, diagnose that event under its applicable procedure before treating SRVO-021 as the primary fault. Motor, feedback and mechanical branches should not be added solely because SRVO-021 is present. They become relevant only when another earlier or associated alarm supports them.

Third, confirm the HRDY and SRDY states using the diagnostic screen or existing maintenance records. The documented SRVO-021 condition requires HRDY to be ON while SRDY remains OFF and no other alarm to explain the state. If the observed status differs, verify the complete alarm record and use the procedure matching the actual condition.

Fourth, inspect configuration-specific connections. Use only the drawings and connector designations for the installed controller and options. Look for incomplete seating, visible damage, contamination, unsupported cable strain or evidence of prior cabinet work. Connector names should not be assumed from another controller arrangement. Exact locations and inspection procedures depend on the confirmed configuration and manual revision.

Fifth, determine whether an instantaneous power interruption occurred at the alarm time. Compare the timestamp with available facility power records, controller history and upstream equipment records. If evidence is unavailable, record that the power-interruption status is unknown rather than treating it as confirmed or excluded.

Sixth, evaluate the emergency-stop unit and servo amplifier according to the applicable maintenance manual. Inspection should follow the manufacturer’s sequence for the exact hardware. SRVO-021 indicates that the commanded magnetic-contactor action was not completed; it does not establish that the complete servo amplifier has failed.

When Repair or Replacement May Be Considered

Professional component testing may be appropriate when configuration checks, alarm chronology and the relevant manual procedure point toward the emergency-stop unit or servo amplifier. Before repair or replacement, match the exact model, part number, hardware revision and connector layout. Also document installed options and auxiliary-axis hardware because superficially similar assemblies may not be interchangeable.

A known-good substitution should be considered only when permitted by the applicable service procedure and site controls. If the evidence supports amplifier inspection, information about FANUC R-30iB servo amplifier repair is available at https://autonews.best/products/fanuc-r-30ib-si-fu-qi-ji-xiu. That service page should not be interpreted as proof that SRVO-021 requires amplifier replacement.

Common Diagnostic Mistakes

Common errors include clearing the event log before recording earlier alarms, omitting Group and Axis, applying a connector map from a different controller configuration, and ordering an amplifier from an incomplete label. Another mistake is expanding immediately into motor, encoder, brake or mechanical troubleshooting without an associated alarm that supports those branches.

A successful reset also does not identify the cause. Record whether the alarm cleared, how the system was restarted and whether recurrence was observed during an authorized verification period. Do not claim resolution solely because motor power returned once.

Information Required for a Repair Inquiry

For a focused assessment, provide the controller model, robot model, complete SRVO-021 text, Group and Axis, full event log, exact alarm time, fault conditions, clear connector photographs and the servo-amplifier label. HRDY and SRDY status is useful when it can be obtained from the diagnostic screen or maintenance records. ZHB is an independent industrial robot inspection, repair and maintenance service provider that also supplies parts to overseas customers; it does not imply FANUC authorization.

Verification After Repair or Replacement

After approved work, confirm that all disturbed connections are secured, protective covers are restored and no tools or loose items remain in the cabinet. Review the alarm history, verify the expected servo-ready transition and conduct restart checks under the applicable manufacturer instructions and site safety procedure. Any motion observation must be performed by competent personnel under controlled conditions. Record the final configuration, repaired or replaced part identification, test conditions and any recurring alarms.

Sources and Update Information

The alarm definition and diagnostic priority used here are based on the FANUC Robot series R-30iB Mate/R-30iB Mate Plus Controller Maintenance Manual, B-83525EN/07, SRVO-021 SRDY off, page 73. FANUC America Corporation is the document owner. Haas Automation hosts the accessible PDF copy at https://www.haascnc.com/content/dam/haascnc/en/service/reference/fanuc-manuals/Fanuc%20Robot%20Series%20R-30iB%20Mate%20+%20Mate%20Plus%20Maintenance%20Manual.pdf.

Conclusion

Effective SRVO-021 diagnosis depends on evidence order rather than immediate parts replacement. Preserve the complete event history, identify any earlier alarm, confirm HRDY and SRDY, inspect only configuration-matched connections, check for an instantaneous power interruption, and then evaluate the emergency-stop unit and servo amplifier under the correct manual.