FANUC Spindle Alarms Explained: SP9017, SP9018, SP9019, SP9020

In today’s fast-paced CNC (Computer Numerical Control) machining industry, precision and efficiency are everything. FANUC systems have earned a global reputation for powering reliable CNC machines across industries—from automotive to aerospace. But like any complex system, spindles can develop issues, often flagged by alarm codes.

In this guide, we’ll break down four common FANUC spindle alarms (SP9017, SP9018, SP9019, SP9020), explain what they mean, and provide insights on troubleshooting and repair.

1. Why FANUC Spindle Alarms Matter

The spindle is the heart of any CNC machine. It drives the cutting tool or the workpiece, and any disturbance in its operation can compromise machining accuracy. FANUC spindle alarms serve as early warning signals, helping operators detect problems before they escalate. By addressing alarms quickly, you can:

• Prevent costly breakdowns

• Minimize production downtime

• Protect spindle components from further damage

• Maintain consistent machining quality

2. Understanding FANUC Spindle Alarm Codes

FANUC CNC systems use a standardized alarm code system to identify problems. Each code corresponds to a specific function or component, making it easier for technicians to pinpoint the issue.

Here’s a closer look at four common spindle alarm codes.

SP9017: Spindle Amplifier ID Abnormality

Meaning: The CNC system failed to recognize the spindle amplifier’s ID.

• The amplifier controls spindle speed and torque.

• If the ID is unreadable or mismatched, the system triggers this alarm.

Possible Causes:

• Incorrect amplifier installation

• Damaged ID circuit inside the amplifier

• Faulty communication between amplifier and CNC control

SP9018: Program ROM Check Error

Meaning: The spindle amplifier’s Read-Only Memory (ROM) contains essential data for operation. If the CNC detects an error during a ROM check, the SP9018 alarm is raised.

Possible Causes:

• Corrupted ROM data

• Aging or defective amplifier hardware

• Power surges damaging ROM circuits

SP9019: Excessive U-Phase Current Offset

Meaning: The CNC detected an abnormal offset in the U-phase current of the spindle motor.

• The spindle motor is three-phase, and the system monitors all three phases.

• A U-phase offset suggests potential amplifier or motor problems.

Alarm Principle:

• Inside the spindle amplifier, the U-phase current detection circuit ensures proper motor operation.

• If the detected value drifts too far from the expected range, SP9019 is triggered.

Typical Causes:

• Faulty U-phase current sensor

• Damaged spindle amplifier circuit board

• Poor electrical connections

SP9020: Excessive V-Phase Current Offset

Meaning: Similar to SP9019, this alarm indicates a V-phase current offset.

Alarm Principle:

• The V-phase current detection circuit inside the amplifier reports abnormal initial values.

• Often linked to hardware failures or sensor malfunctions.

Typical Causes:

• Damaged amplifier circuit board

• Sensor failure due to long-term wear

• Loose or aging electrical connections

3. Real-World Repair Cases

Case 1: SP9019 Alarm

• Problem: U-phase current sensor failure in the spindle amplifier

• Solution: Sensor replacement restored normal operation

Case 2: SP9020 Alarm

• Problem: Damaged circuit board in spindle amplifier

• Solution: Circuit board replacement cleared the alarm

4. Best Practices for Handling FANUC Spindle Alarms

• Do not attempt DIY repairs unless you have electronic maintenance expertise

• Inspect connections before assuming component failure

• Contact professional CNC technicians for amplifier or motor repairs

• Schedule preventive maintenance to reduce future alarm risks

Final Note: FANUC spindle alarms are not random—they are designed to protect your CNC investment. Understanding alarms like SP9017, SP9018, SP9019, and SP9020 helps you act quickly, minimize downtime, and keep your machines running at peak performance.

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