FANUC SP9075 Alarm 75: Spindle ROM CRC Error and Troubleshooting

FANUC SP9075 means that the spindle amplifier detected an error while checking the integrity of spindle software stored in ROM. The CNC displays SP9075 / CRC ERROR, while the spindle amplifier displays alarm 75. FANUC identifies this as a Dual Check Safety self-diagnostic alarm and directs technicians to replace the applicable spindle-amplifier control printed-circuit board or the complete spindle amplifier.

Alarm 75 is not a CNC machining-program error, lost machine backup, motor-feedback problem, or serial communication CRC error. It specifically concerns the ROM CRC test inside the spindle system.

For the surrounding alarm numbers, see the FANUC Spindle Alarm Codes SP9034–SP9092.

What Does FANUC SP9075 Mean?

CRC stands for cyclic redundancy check. It is an integrity check used to determine whether stored data still matches the expected content. In the FANUC Dual Check Safety system, safety-related data stored in ROM is checked at power-on and after power-on. FANUC identifies separate alarms according to the processor or software area in which an abnormal result is found.

For the spindle software, that result is SP9075 / spindle alarm 75.

The alarm does not prove that an operator changed the software, and it should not be diagnosed as a normal parameter-setting mistake. It means that the spindle system could not validate the ROM content used by the safety-related control. FANUC therefore treats it as an internal spindle-amplifier hardware or control-board condition.

SP9075 Occurs Only With Dual Check Safety

FANUC states that alarm 75 can be issued only when Dual Check Safety is in use. The function performs independent monitoring and internal self-tests so that a fault affecting safety-related processing can be detected.

The Dual Check Safety manuals distinguish the CRC results by software area:

This distinction prevents a spindle ROM error from being misdiagnosed as a CNC BASIC ROM, servo ROM, or PMC software fault. Always use the complete alarm text and the amplifier display.

Do not disable Dual Check Safety, bypass the alarm, or change safety parameters to make the alarm disappear. SP9075 indicates that the system cannot confirm the integrity of safety-related spindle software.

1. Confirm SP9075 and Amplifier Alarm 75

Before removing any hardware, confirm that:

• The CNC alarm screen shows SP9075 or CRC ERROR for the spindle.

• The spindle amplifier status display shows 75.

• The alarm is assigned to the expected spindle amplifier.

• The CNC is not reporting a separate boot-system, servo, PMC, communication, or encoder CRC alarm.

Record the alarm screen before switching off the machine. Also record:

• Complete CNC series and model

• Exact spindle amplifier or SPM model, including every suffix

• Spindle software series and edition, when available

• Dual Check Safety configuration

• Spindle number and amplifier position in a multi-spindle system

• Whether the alarm appeared at power-up or after the machine had been operating

• Whether an amplifier, control PCB, CNC board, or safety component was recently replaced

• Any alarm displayed at the same time

CRC alarms exist in several FANUC subsystems. The words “CRC error” alone do not identify the faulty unit. A confirmed SP9075 requires the spindle alarm number and amplifier indication.

2. Understand When the CRC Test Runs

FANUC's Dual Check Safety documentation states that the safety-related ROM data is checked at power-on and after power-on. SP9075 can therefore be detected during startup or after the system has entered operation.

The occurrence time can be recorded for service history, but it does not change FANUC's official repair direction:

Repeatedly clearing or power-cycling the alarm does not repair a failed ROM integrity check. A controlled restart may be used only as part of the machine builder's confirmation procedure.

3. Follow the Replacement Instruction for the Exact Amplifier Series

The approved replaceable unit differs between FANUC hardware generations:

These instructions describe the same internal fault but reflect differences in amplifier construction and approved service practice. Do not assume that a control PCB can be replaced separately in every spindle amplifier.

For a series that supports control-board replacement, install only the exact compatible board and follow the applicable board-replacement procedure. When the manual specifies unit replacement, replace the complete spindle amplifier rather than improvising an in-machine ROM or board repair.

4. Do Not Add Unrelated Troubleshooting Steps

FANUC's alarm 75 procedure does not direct technicians to:

• Reload CNC machining programs

• Restore machine SRAM or parameter backups as the repair

• Reinstall spindle software in the field

• Change Dual Check Safety parameters

• Modify the PMC ladder

• Replace the CNC main board

• Inspect motor phase order or power leads

• Replace the motor sensor or feedback cable

• Test magnetic contactors

• Reduce spindle load

• Replace a cooling fan

These actions belong to different alarms or service procedures. SP9075 is not a generic data-loss message. Restoring a CNC backup cannot correct an abnormal CRC result in spindle software stored on the spindle-amplifier hardware.

Do not attempt an unofficial ROM reprogramming procedure. If a specific FANUC service bulletin or machine builder instruction applies to the exact hardware, follow that controlled procedure; otherwise, the published alarm 75 action is hardware replacement.

5. Select the Correct Control PCB or Spindle Amplifier

Before replacement, verify:

• Complete FANUC part number and every suffix

• Amplifier generation and hardware specification

• Rated spindle-amplifier capacity

• CNC and spindle motor compatibility

• Spindle software series and supported edition

• Dual Check Safety capability

• Hardware ID and machine configuration requirements

• Connector layout and amplifier position

Do not select a replacement by appearance, output rating, or base model alone. An amplifier with an incompatible suffix, control board, or spindle software can produce a different startup, axis-data, software, or safety alarm.

If only the control PCB will be replaced, confirm that the board is approved for the exact amplifier and that its software and hardware specification match the machine. Preserve all original connector positions, mounting hardware, and documented settings.

For replacement options, browse FANUC servo, spindle, and power drives or send the complete amplifier model and suffix to REACO CNC for a compatibility check.

6. Replace the Specified Hardware Safely

Only qualified personnel should replace a spindle-amplifier control board or complete amplifier. Isolate machine power and follow the DC-link discharge time, stored-energy warnings, electrostatic-discharge precautions, and removal procedure in the applicable FANUC and machine builder manuals.

Before removing the original unit:

1. Preserve the approved machine configuration and available backups.

2. Photograph or label every connector and amplifier position.

3. Record the full part number, suffix, spindle software information, and any switch or jumper settings.

4. Confirm that the DC link has discharged to the specified safe level.

5. Protect the original and replacement control electronics against electrostatic discharge.

Do not transfer an unidentified control board between amplifiers merely because its physical dimensions and connectors appear similar. The wrong board or software specification can prevent the Dual Check Safety configuration from operating correctly.

7. Complete Post-Replacement Safety Verification

Because SP9075 is associated with Dual Check Safety, clearing alarm 75 is only one part of the repair. FANUC requires safety parameters and safety functions to be verified after a relevant part is replaced.

After installing the correct hardware:

• Power up the machine according to the machine builder's procedure.

• Confirm that SP9075 and amplifier alarm 75 no longer appear.

• Confirm that no new CRC, hardware-ID, axis-data, compatibility, or safety alarm is displayed.

• Verify that the amplifier is assigned to the correct spindle.

• Compare applicable safety parameters with the approved machine record.

• Perform the required Dual Check Safety acceptance or functional checks.

• Test spindle operation through the machine builder's commissioning sequence.

• Record the replacement part number, spindle software information, and test results.

Do not return the machine to production until the required safety validation is complete. A cleared display does not by itself prove that the entire safety system is functioning correctly.

Difference Between SP9016, SP9074, SP9075, SP9076, and SP1225

The word “test” or “CRC” appears in several FANUC alarms, but each identifies a different failure.

For the related RAM-test condition, see the FANUC SP9016 Alarm 16: Dual Check Safety RAM Error.

Do not replace communication cables for SP9075 merely because another alarm also uses the term CRC. Confirm the exact alarm number and affected subsystem.

FANUC SP9075 Diagnostic Table

What Not to Do

• Do not disable or bypass Dual Check Safety.

• Do not change safety parameters to suppress the CRC alarm.

• Do not confuse spindle ROM with CNC program memory or machine SRAM.

• Do not restore a CNC backup as the official repair for SP9075.

• Do not attempt an unsupported ROM reflash or board modification.

• Do not replace motor, feedback, cooling, or contactor components without evidence from another alarm.

• Do not replace a CNC main board solely because the message contains “CRC.”

• Do not install an amplifier or control PCB without verifying the full part number, suffix, software, and DCS compatibility.

• Do not return the machine to service without the required post-replacement safety checks.

Recommended Troubleshooting Order

1. Confirm SP9075 on the CNC and alarm 75 on the spindle amplifier.

2. Record the CNC, complete amplifier model and suffix, spindle software, DCS configuration, occurrence time, and accompanying alarms.

3. Confirm that the alarm is a spindle ROM CRC error rather than a CNC, servo, PMC, or communication CRC alarm.

4. Consult the maintenance manual for the exact amplifier generation to identify the approved replaceable unit.

5. Verify the complete specification and compatibility of the replacement control PCB or spindle amplifier.

6. Isolate machine power and replace the specified hardware according to the applicable electrical-safety procedure.

7. Restore and verify the approved configuration without making unrelated parameter or ladder changes.

8. Confirm that alarm 75 is cleared and no new compatibility or safety alarm appears.

9. Complete the required Dual Check Safety acceptance checks and spindle commissioning tests.

10. Diagnose any new alarm by the number actually displayed.

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 75

• FANUC AC Servo Motor αi-B Series, AC Spindle Motor αi-B/βi-B Series, Servo Amplifier αi-B Series Maintenance Manual, B-65515EN/01, Alarm Code 75

• FANUC Series 30i-A Dual Check Safety Operator's Manual, B-64004EN series, CRC Check Function and SP9075

• FANUC Series 0i-D Dual Check Safety Connection Manual, B-64303EN-4 series, SP9075 alarm list

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 SP9075 Alarm 75?

REACO CNC provides independent testing, repair, compatibility checking, and replacement support for FANUC spindle amplifiers and control printed-circuit boards. Send the CNC alarm screen, spindle-amplifier display, complete CNC model, exact amplifier model and suffix, spindle software information, and details of when the alarm appeared.

Visit the FANUC Technical Support Center or contact REACO CNC for assistance.

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