FANUC SRVO-021 SRDY OFF Robot Repair Guide

FANUC SRVO-021 SRDY OFF 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. The potentially involved systems include controller connections, the emergency-stop unit, the servo amplifier, and the incoming power history. Before industrial robot repair begins, record the complete code, Group, Axis, event sequence, and controller model. This alarm alone does not confirm servo amplifier damage, so replacement should not be the first diagnostic action.

Symptoms and Scope

This guide applies specifically to FANUC R-30iB Mate and R-30iB Mate Plus controllers within the scope of FANUC maintenance manual B-83525EN/07. Connector locations, circuit arrangements, and inspection procedures depend on the installed controller configuration and options. Technicians must use the maintenance documentation matching the actual system.

The alarm definition requires three conditions: HRDY is ON, SRDY remains OFF, and no other alarm accounts for the state. The controller commanded the servo amplifier magnetic contactor to turn on, but the expected ready state was not established. This observation does not independently identify whether the cause is a connection, an instantaneous power interruption, the emergency-stop unit, or the servo amplifier.

Do not extend the diagnosis to the motor, feedback-related components, or mechanical transmission unless an earlier or associated alarm provides evidence for that branch.

Information to Record First

Preserve the event information before resetting alarms or cycling controller power. Alarm history often determines whether SRVO-021 is the primary event or a consequence of an earlier condition.

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 this FANUC alarm, also record Group and Axis exactly as displayed. Identify the robot model, controller model, software information available on the controller, and the servo-amplifier label. Note whether the event occurred during startup, servo enable, program execution, or recovery from a stop. Do not repeatedly enable the robot merely to reproduce the alarm.

Safety and Preparation

Follow the FANUC maintenance manual for the installed controller and the factory’s lockout, electrical safety, and stored-energy procedures. Work involving controller power circuits, emergency-stop circuits, or internal connections must be performed only by suitably competent personnel.

Before inspecting connections, place the robot in a safe condition and account for gravity-loaded axes, tooling, workpieces, and external axes. Do not bypass safety devices or alter safety-critical parameters to clear SRVO-021. Unsupported live measurements or contactor manipulation can expose personnel and equipment to serious risk.

SRVO-021 Robot Maintenance Diagnostic Sequence

1. Record the complete event. Capture SRVO-021 SRDY OFF with its Group and Axis information, exact time, operating stage, and reset behavior. The input is the alarm screen and event history; the decision is whether the displayed information is complete enough to identify the affected group. If Group or Axis data is missing, retrieve it before selecting a hardware inspection path.
2. Identify any earlier alarm. Review the full event log in chronological order rather than examining SRVO-021 alone. If another alarm occurred first and explains why servo readiness was withheld, diagnose that earlier alarm under its applicable procedure. If no other alarm explains the state, continue with the SRVO-021 sequence. Do not assume the latest alarm is the initiating fault.
3. Confirm HRDY and SRDY status. Use the appropriate diagnostic screen or maintenance record to establish that HRDY is ON while SRDY remains OFF. If these conditions are not present, the verified SRVO-021 definition may not describe the current state, and the displayed alarms and controller documentation must be reviewed again. Status interpretation should be performed without bypassing interlocks.
4. Inspect configuration-specific connections. With the system safely isolated as required by the applicable procedure, inspect the relevant controller and servo-system connections for incomplete seating, visible damage, contamination, or configuration mismatch. Compare the installed wiring and connector layout with the exact controller documentation. Specific connector designations should not be assumed from another cabinet or manual revision.
5. Check for an instantaneous power interruption. Review plant records, controller history, and available maintenance information for evidence that an instantaneous power interruption occurred at the alarm time. If supporting evidence exists, investigate that event according to the facility’s electrical procedures before condemning robot hardware. If the information is unavailable, record that uncertainty rather than treating power interruption as confirmed.
6. Evaluate the emergency-stop unit and servo amplifier. If the previous steps do not identify an explanation, follow the controller-specific manual procedures for evaluating the emergency-stop unit and servo amplifier. Inspection results must be interpreted together with the event log, status information, configuration, and component identifiers. SRVO-021 does not by itself prove that either assembly is defective.

When Repair or Replacement May Be Considered

Professional testing may be appropriate when inspections identify physical damage, repeatable internal malfunction, or results outside the applicable manufacturer procedure. Before selecting a spare, match the exact servo-amplifier model, FANUC part number, hardware revision, supported configuration, and connector layout. A visually similar unit may not be compatible.

For component-level support, the FANUC R-30iB servo amplifier repair page provides relevant service information: https://autonews.best/products/fanuc-r-30ib-si-fu-qi-ji-xiu. 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.

For one repair inquiry, provide the controller model, robot model, complete SRVO-021 SRDY OFF event with Group and Axis, full event log, alarm time, clear connector photographs, and the servo-amplifier label. Include HRDY and SRDY status only when it can be obtained safely from the diagnostic screen or existing maintenance records.

Verification After Repair or Replacement

After approved work is completed, confirm that all inspected connections are restored correctly, protective covers are installed, tools are removed, and safety devices remain functional. Review the alarm history and verify the controller reaches the expected ready state using the applicable FANUC startup procedure.

Any motion observation must be performed only by competent personnel under controlled conditions and in accordance with manufacturer operating information and site safety procedures. Begin with the site-approved verification process rather than immediately returning the robot to unrestricted production. Confirm that SRVO-021 does not recur during the authorized checks and document the final configuration, repaired or replaced component, and verification result.

Common Diagnostic Mistakes

Common errors include replacing the servo amplifier solely because SRDY remained OFF, ignoring an earlier alarm, omitting Group and Axis information, and using connector references from the wrong controller configuration. Resetting or power cycling before preserving the event log can also remove valuable sequence information. Expanding immediately into motor, feedback, or mechanical troubleshooting creates unnecessary work unless another alarm supports those paths.

Sources and Update Information

The alarm definition and diagnostic priority are based on FANUC Robot series R-30iB Mate/R-30iB Mate Plus Controller Maintenance Manual B-83525EN/07, page 73, owned by FANUC America Corporation. An accessible PDF copy is hosted by Haas Automation 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. Always confirm that the manual revision and controller configuration match the installed equipment.

Conclusion

Effective SRVO-021 troubleshooting depends on evidence, not premature part replacement. Preserve the complete event, identify earlier alarms, confirm HRDY and SRDY, inspect configuration-specific connections, check for an instantaneous power interruption, and only then evaluate the emergency-stop unit and servo amplifier under the matching FANUC procedure.