FANUC SP9077 Alarm 77: Axis Number Check Mismatch

FANUC SP9077 means that the spindle amplifier's axis-number check result does not match the CNC's axis-number check result. The CNC displays SP9077, while the spindle amplifier displays alarm 77. This alarm can occur only when FANUC Dual Check Safety is in use.

SP9077 is a safety cross-check alarm between the CNC CPU and spindle-amplifier CPU. It is not the same as an ordinary program axis-selection error, an invalid spindle command, or a motor feedback fault. FANUC's official procedure specifies replacement of the CNC CPU card or the applicable spindle-amplifier hardware. The exact drive-side part depends on the amplifier series.

For other alarms in this range, see the FANUC Serial Spindle Alarm Codes SP9034–SP9092.

What Does FANUC SP9077 Mean?

Dual Check Safety does not rely on a single processor for its safety judgment. Safety-related processing and data are checked independently, and the results are compared. For SP9077, the CNC side and spindle-amplifier side each check the spindle axis number. The alarm is generated when their judgments do not agree.

The phrase axis number in this alarm identifies the spindle assignment being used in the safety cross-check. It does not mean that the machine's physical axis moved to an incorrect position. It also does not identify a spindle encoder, motor phase, position coder, or mechanical indexing problem.

FANUC's Dual Check Safety alarm list describes SP9077 as MISMATCH RESULT OF AXIS NUMBER CHECK. The αi and αi-B maintenance manuals provide the same detection condition and direct the technician toward the CNC CPU card or spindle-amplifier electronics.

SP9077 Is a Dual Check Safety Cross-Check Alarm

SP9077 can be issued only when Dual Check Safety is active. The safety system compares judgments made by the CNC CPU and the spindle CPU. When the two results differ, the comparison can no longer provide the required independent confirmation, so the system reports a safety alarm.

The FANUC Dual Check Safety diagnosis pages can help confirm the alarm category. On supported CNCs, the DUAL CHECK diagnosis area includes a spindle-status screen that shows the cause of a spindle-related cross-check alarm. This screen may support diagnosis, but it does not replace the hardware action stated in the applicable maintenance manual.

Do not bypass Dual Check Safety or disable the affected safety monitoring to keep the machine operating. The mismatch concerns the integrity of the safety comparison itself.

1. Confirm SP9077 and Amplifier Alarm 77

Before replacing hardware, verify the exact displays:

• The CNC alarm screen shows SP9077 or the corresponding SSPA:77 message.

• The spindle amplifier status display shows 77.

• The machine is equipped and configured with FANUC Dual Check Safety.

• The alarm is assigned to the spindle system rather than to a servo axis or PMC safety channel.

• Any simultaneous CNC or DCS alarm is recorded before power is removed.

If the control supports it, review the Dual Check Safety spindle-status diagnosis screen and record the displayed cross-check information. Do not change data merely because the diagnostic screen identifies the spindle involved.

Also record:

• The complete CNC series and model

• The CNC CPU card part number and revision

• The complete spindle amplifier or SPM part number, including every suffix

• The amplifier series and hardware revision

• The spindle software series and edition, when available

• The configured spindle number and machine path

• Whether a CPU card, spindle amplifier, control board, or system configuration was recently changed

• Whether the alarm appeared at power-up or during normal operation

These details are needed to identify the applicable manual and the correct replacement hardware.

2. Use the Correct FANUC Replacement Instruction

FANUC's drive-side repair instruction differs by amplifier family:

The manuals list the two fault locations as alternatives. They do not state a universal rule that the spindle board must always be replaced first or that the CNC CPU card must always be replaced first.

Use the machine's exact hardware configuration, available diagnostic evidence, and controlled substitution with known-good compatible parts to determine which side is faulty. If board-level replacement is not supported for the installed amplifier series, replace the complete spindle amplifier rather than adapting a procedure from another series.

3. Do Not Treat SP9077 as an Ordinary Parameter Alarm

It is tempting to interpret “axis number mismatch” as proof that an operator entered an incorrect axis or spindle parameter. FANUC's alarm 77 procedure, however, does not instruct the technician to edit an axis-number parameter. The stated action is replacement of the CNC CPU card or the applicable spindle-amplifier hardware.

Do not change the following without separate evidence and the correct commissioning procedure:

• CNC axis assignments

• Spindle numbers or motor-number assignments

• Dual Check Safety parameters

• Path or machine-group configuration

• PMC ladder logic

• Spindle speed parameters

• Motor initialization data

• Feedback or position-coder parameters

If SP9077 appeared immediately after an authorized CPU, amplifier, or configuration replacement, verify that the installed hardware, software, and restored data match the machine's approved records. This is a commissioning check, not permission to experiment with safety parameters.

Blindly changing protected safety data can create an additional mismatch, cause another DCS alarm, or invalidate the machine's safety validation.

4. Distinguish SP9077 From Configuration Alarm SP9070

SP9070 and SP9077 can both sound like axis-assignment problems, but FANUC defines them differently:

Do not apply the alarm 70 connection-and-setting procedure to alarm 77 unless SP9070 or other evidence is also present. Always work from the exact alarm number shown on the amplifier.

5. Select Compatible Replacement Hardware

For a spindle-amplifier control board or complete amplifier, verify:

• Full FANUC part number and every suffix

• Amplifier series and hardware specification

• Control printed-circuit board number, when board replacement is supported

• Spindle software compatibility

• Dual Check Safety support

• Compatibility with the CNC, spindle motor, and machine configuration

• Connector arrangement and machine-builder installation requirements

For a CNC CPU card, verify:

• Complete CNC model and CPU card part number

• Hardware revision and supported system software

• Option and memory compatibility

• Dual Check Safety compatibility

• Machine-specific data backup and restoration requirements

Do not select a replacement by appearance, connector count, base model, or output rating alone. An incompatible board or amplifier can introduce a different hardware, software, axis-assignment, or safety alarm.

If replacement drive hardware is required, browse FANUC servo, spindle, and power drives or send REACO CNC the complete part number for a compatibility check.

6. Back Up the CNC Before CPU Card Replacement

Replacing a CNC CPU card can affect system software, options, parameters, PMC data, offsets, macro variables, and machine-specific safety information. Before removing the card, follow the machine builder's approved backup procedure and record the existing configuration.

The backup and restoration plan should account for:

• CNC and spindle parameters

• PMC ladder and PMC data

• Tool offsets and work offsets

• Macro variables and machine-builder data

• System software and option compatibility

• Dual Check Safety parameters and protected safety records

Do not assume that a general CNC backup automatically covers every protected or machine-builder-specific safety item. Restoration and verification must follow the documentation for the exact CNC and machine.

7. Replace the Suspected Hardware Safely

Only qualified personnel should replace a CNC CPU card, spindle-amplifier control board, or complete spindle amplifier.

Before beginning work:

1. Stop the machine using the approved procedure.

2. Isolate and lock out the main power.

3. Wait the specified DC-link discharge time.

4. Verify that the required circuits are de-energized.

5. Use electrostatic-discharge precautions when handling circuit boards.

6. Record every connector, board position, switch, and removable configuration item.

7. Preserve the original hardware until the repair and safety validation are complete.

Install only a known compatible replacement. Do not transfer software devices, memory modules, jumpers, or option parts unless the applicable FANUC or machine-builder procedure specifically requires it.

8. Validate Dual Check Safety After the Repair

SP9077 may disappear after the faulty CPU card or drive hardware is replaced, but alarm clearance alone is not sufficient. FANUC requires the safety parameters and safety functions to be verified after replacement of a safety-related component.

After replacement:

• Confirm that SP9077 and amplifier alarm 77 no longer appear.

• Confirm that no new software, option, axis-assignment, hardware, or DCS alarm is displayed.

• Verify the CNC and spindle configuration against the approved machine record.

• Verify all applicable safety parameters.

• Perform the prescribed Dual Check Safety function check or acceptance test.

• Confirm the required safe-stop and spindle-monitoring behavior.

• Test normal spindle operation only after the safety checks pass.

• Record the replacement, restored data, parameter verification, and test results.

The safety-function check must be carried out by an authorized person familiar with the machine's safety design. Do not return the machine to production solely because a reset or replacement cleared the alarm display.

SP9077 Compared With Related Dual Check Safety Alarms

Do not diagnose every mismatch alarm as SP9077. The number identifies which independently calculated result failed to agree.

For a related internal safety-test alarm, see the FANUC SP9016 Alarm 16 guide.

FANUC SP9077 Diagnostic Table

What Not to Do With SP9077

• Do not bypass or disable Dual Check Safety.

• Do not change spindle or axis numbers by trial and error.

• Do not edit protected safety parameters merely to clear the alarm.

• Do not diagnose alarm 77 as a motor, encoder, feedback-cable, or phase-sequence fault.

• Do not replace only the drive control board when the applicable series requires complete-amplifier replacement.

• Do not install a CNC CPU card without a verified backup and compatibility plan.

• Do not assume the manuals prescribe a universal board-first or CPU-first replacement order.

• Do not release the machine before the required safety-function test is documented.

Recommended Troubleshooting Order

1. Confirm SP9077 on the CNC and alarm 77 on the spindle amplifier.

2. Verify that Dual Check Safety is in use.

3. Record all simultaneous alarms and the Dual Check spindle-status diagnosis, when supported.

4. Record the exact CNC, CPU card, spindle amplifier, control-board, and software information.

5. Check whether the alarm followed an authorized hardware or configuration change.

6. Identify the maintenance manual for the exact amplifier series.

7. Determine whether the drive-side action is control-board replacement or complete-amplifier replacement.

8. Use controlled diagnosis or known-good compatible hardware to identify the CNC CPU side or spindle-amplifier side.

9. Back up the machine completely before CNC CPU card replacement.

10. Isolate power and replace the confirmed or most strongly supported fault location.

11. Restore and verify the approved machine configuration.

12. Perform and document the required Dual Check Safety function test before returning the machine to service.

Technical References

• FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/04, Alarm Code 77

• FANUC Series 30i-A Dual Check Safety Operator's Manual, B-64004EN/02, Spindle/CNC Cross Check and SP9077

• FANUC Servo Amplifier αi-B Series Maintenance Manual, B-65515EN/01, Alarm Code 77 (SP9077)

Always use the manual edition that applies to the exact CNC, spindle amplifier, spindle software, Dual Check Safety configuration, and machine.

Need Help With FANUC SP9077 Alarm?

REACO CNC provides independent testing, repair, compatibility checking, and replacement support for FANUC CNC CPU cards, spindle-amplifier control boards, and complete spindle amplifiers. Send us the CNC alarm screen, amplifier display, complete CNC model, CPU card number, full spindle amplifier model and suffix, software information, and details of when the alarm occurs.

Visit the FANUC Technical Support Center for more FANUC alarm guides, or contact REACO CNC for assistance.

Reference Source: Beijing FANUC. This article is based on FANUC technical documentation. The applicable replacement, data-restoration, and safety-validation procedure depends on the exact CNC, spindle amplifier, software, Dual Check Safety configuration, and machine.