FANUC SP9024 Alarm 24: Serial Transfer Error Troubleshooting

FANUC SP9024 means that an error was detected in serial communication data transferred between the CNC and the spindle amplifier. The CNC may show SP9024 / SSPA:24 SERIAL TRANSFER ERROR, while the spindle amplifier displays 24.

There is one important exception: FANUC states that alarm 24 can also appear when the CNC power is off. If it appears only during normal CNC power-off, it does not indicate a failure. If the CNC is powered normally and the alarm remains, check the CNC-to-spindle communication path, cable routing and electrical noise before replacing hardware.

For the surrounding spindle alarm numbers, see the FANUC Serial Spindle Alarm Codes SP9001–SP9033.

What Does FANUC SP9024 Mean?

The spindle amplifier and CNC exchange control data through a serial communication link. Alarm 24 is generated when that transferred data is abnormal or when communication from the CNC is no longer available.

FANUC B-65285EN/04 describes alarm 24 as an error in serial communication data transferred between the CNC and spindle amplifier. The Series 0i-D/0i Mate-D alarm table describes the related condition as CNC power being turned off, either through normal power-off or because the cable is broken.

These descriptions are not contradictory. The amplifier cannot receive normal CNC communication in either case:

• During an intentional CNC power-off, alarm 24 can be a normal temporary indication.

• With the CNC powered, a broken cable, excessive electrical noise or a communication hardware fault can produce a real alarm.

The timing of the display must therefore be recorded before any component is replaced.

Main Causes of FANUC Alarm 24

FANUC documentation identifies the following diagnostic directions:

• The CNC is powered off. Alarm 24 during normal CNC power-off is not a failure.

• The electrical communication cable is affected by noise. Cable length, connection condition and installation method may not meet the applicable specification.

• The communication cable is routed with a motor power lead. Bundling the serial communication cable with power wiring can introduce interference.

• The communication cable is faulty or disconnected. A damaged conductor, connector or cable can interrupt communication.

• An optical link component is faulty. Where an optical I/O link adapter is used, the adapter or optical cable may be defective.

• Motor-specific parameters are incorrect on an applicable βiSVSP system. This additional check appears in the βiSVSP maintenance procedure and should not be applied automatically to every amplifier series.

• The spindle amplifier or its control printed-circuit board is faulty. Consider this after the cable and installation conditions have been checked.

• The CNC serial-spindle board or module is faulty. This is an end-stage hardware direction after the external communication path and amplifier side have been isolated.

Do not begin by changing spindle orientation, position-sensor or cutting parameters. Those settings are not identified as general causes of alarm 24.

1. Confirm Whether Alarm 24 Is a Normal Power-Off Indication

Before troubleshooting, determine exactly when the amplifier displays 24:

• If it appears only after the CNC is intentionally switched off, FANUC states that it is not a failure.

• If the CNC display and operation are normal but SP9024 remains active, treat it as a communication fault.

• If the CNC loses power unexpectedly, diagnose the CNC power interruption as well as the communication alarm.

• If the alarm appears intermittently while the machine is running, record whether another machine, contactor, spindle motor or high-power device was operating at the same time.

Photograph the CNC alarm screen and spindle amplifier display before cycling power. Also record:

• The complete CNC series and model

• The exact spindle amplifier model and every suffix

• The spindle software series and edition when available

• Whether the connection is electrical or uses an optical I/O link adapter

• When the alarm occurs and whether the communication cable was recently moved or replaced

• Any recent CNC, amplifier, control-board or cabinet wiring work

Some FANUC series may map amplifier alarm 24 to a CNC number other than SP9024, such as a series-dependent serial spindle alarm. Confirm the amplifier display and use the maintenance manual for the installed system.

2. Inspect the CNC-to-Spindle Communication Cable

Isolate machine power and follow the machine builder's electrical-safety procedure before touching cabinet wiring or amplifier connectors. Wait for the required DC-link discharge period and confirm the safe electrical condition specified in the applicable FANUC manual.

Check the communication path for:

• A loose or incompletely inserted connector

• Bent, damaged, contaminated or corroded contacts

• A cable that was pulled, crushed or sharply bent

• Damage near cabinet doors, cable clamps or moving sections

• A cable length or type that does not meet the applicable FANUC connection specification

• Recent wiring changes that altered the original route

Technician documentation may describe the communication path as JA41—JA7B on a particular configuration. Connector designations are not universal across all FANUC CNC and spindle amplifier series. Use those labels only when the machine electrical drawing and the applicable FANUC connection manual identify them for the installed hardware.

Do not perform continuity checks through connected CNC or amplifier electronics unless the exact maintenance procedure permits it. Disconnect and test cables only with the required power isolation and component-protection precautions.

3. Separate the Communication Cable From Power Wiring

FANUC specifically identifies noise caused by routing the communication cable together with the motor power lead.

Verify that:

• The CNC-to-spindle communication cable is routed separately from motor, spindle and other high-current power cables.

• The cable follows the separation and grounding requirements in the applicable FANUC amplifier description manual and machine electrical design.

• Shielding, clamps and cabinet grounding have not been removed or altered.

• Excess cable is not coiled beside contactors, reactors, drives or motor power conductors.

If the alarm began after cabinet rewiring or installation of another high-power device, compare the current routing with the original machine drawing. Restore the approved routing rather than adding unverified grounding or shielding modifications.

4. Replace the Communication Cable or Optical Link Component

If the connection and routing are correct but SP9024 remains, replace the CNC-to-spindle communication cable with the exact specified type.

Before replacement, verify:

• The correct cable specification and length

• The connector type and pin arrangement at both ends

• Whether the installed system uses an electrical cable or optical link arrangement

• The original routing, shielding and clamp positions

Where an optical I/O link adapter is installed, FANUC states that the adapter or optical cable may be faulty. Inspect and substitute only the components used by the actual configuration. Do not assume that every alarm 24 system has an optical link.

After replacement, restore all cable supports and protective covers before powering the machine. If the alarm clears, retest under the operating condition that previously caused the fault.

5. Check Motor-Specific Parameters Only When the Manual Requires It

The FANUC βiSVSP maintenance procedure includes checking motor-specific parameters for alarm 24. The αi SPM procedure in B-65285EN/04 does not list parameter checking as a general step.

For an applicable βiSVSP system:

1. Back up the current CNC and spindle data.

2. Record the complete spindle motor and amplifier models.

3. Compare the motor-specific parameters with the exact B-65280 series parameter manual and the machine builder's original data.

4. Determine whether the alarm began after parameter initialization, restoration or control replacement.

Do not initialize or copy spindle parameters from a similar machine simply to test alarm 24. Apply this step only when it is required by the manual for the installed series and supported by the original machine data.

6. Isolate Spindle Amplifier and CNC Hardware Faults

If CNC power is stable, cable routing and length are correct, and a confirmed good communication cable or optical link does not clear the alarm, the fault may be in the spindle amplifier or CNC.

FANUC lists the hardware actions in this order:

1. Replace the spindle amplifier or its control printed-circuit board according to the applicable series procedure.

2. If the fault remains after the amplifier side has been confirmed, replace the CNC board or module related to the serial spindle.

Before any replacement, verify the complete FANUC part number, every suffix, board number, software compatibility and machine configuration. Do not select a board or amplifier only by physical appearance or connector layout.

Replacing a CNC board may require data backup, restoration and machine-specific commissioning. Preserve all available CNC, PMC and spindle data before authorized replacement work. This step should be performed by qualified personnel using the procedure for the exact CNC.

If a spindle amplifier replacement is required, browse FANUC servo, spindle and power drives or send REACO CNC the complete amplifier model and suffix for a compatibility check.

Difference Between SP9024 and Alarm 27

Both alarms can involve communication cables, but they refer to different links:

Do not replace a spindle position coder solely because alarm 24 is displayed. Confirm whether the failed link is on the CNC side or sensor side of the spindle amplifier.

FANUC SP9024 Diagnostic Table

Recommended Troubleshooting Order

1. Confirm the CNC alarm and amplifier display 24.

2. Determine whether 24 appears only because the CNC has been switched off normally.

3. If the CNC lost power unexpectedly, diagnose the CNC power interruption.

4. Record the complete CNC, amplifier, cable and software information.

5. Isolate power and inspect the CNC-to-spindle communication cable and connectors.

6. Verify the approved cable type, maximum length and connection conditions.

7. Separate the communication cable from motor and other power wiring.

8. Replace the exact communication cable; check the optical adapter and optical cable only when installed.

9. For an applicable βiSVSP system, verify motor-specific parameters using the exact manual and original data.

10. If the alarm remains, test or replace the spindle amplifier/control board, then the CNC serial-spindle board or module.

11. Retest the machine safely and diagnose any new alarm separately.

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 24

• FANUC Series 0i-D/0i Mate-D Maintenance Manual, B-64305EN/03, SP9024 alarm list

• FANUC AC Servo Motor βi Series, AC Spindle Motor βi Series, Servo Amplifier βi Series Maintenance Manual, B-65325EN/02, Alarm Code 24

• FANUC Servo Amplifier αi Series Descriptions, B-65282EN, electrical communication-cable installation requirements

• FANUC Servo Amplifier βi Series Descriptions, B-65322EN, βiSVSP cable installation requirements

• Beijing FANUC SP9024 technical guidance, serial transfer error troubleshooting

Always use the manual edition and connection drawing that apply to the exact CNC, spindle amplifier, communication method, software and machine configuration.

Need Help With FANUC SP9024 Alarm?

REACO CNC provides independent FANUC spindle communication diagnosis, amplifier testing, repair and replacement support. Send us the CNC alarm screen, amplifier display, complete CNC model, exact spindle amplifier model and suffix, cable or connector labels shown in the machine drawing, alarm timing and details of recent wiring or hardware work.

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 cable, parameter and hardware procedure depends on the exact CNC, spindle amplifier, communication link and machine configuration.