FANUC SP9006 Alarm: Causes, Diagnosis, and Repair Guide

In FANUC CNC systems, the SP9006 alarm indicates a thermal relay disconnection, most often caused by an issue with the motor temperature sensor. This sensor typically uses a Negative Temperature Coefficient (NTC) thermistor, a component whose resistance decreases as temperature rises.

Understanding NTC Thermistors in FANUC Systems

NTC thermistors are commonly used in industrial motor systems to monitor temperature. These components have a standard resistance value at 25°C, which decreases as the temperature increases. In FANUC systems, the NTC thermistors usually have a nominal resistance of 40kΩ at 25°C.

For comparison, an NTC thermistor with a 10kΩ rating at 25°C may show the following resistance at other temperatures:

Resistance Formula

The resistance of an NTC thermistor at a given temperature can be approximated using this formula:

R = R₀ × e^(-B/T)

Where:

• R = resistance at temperature T (in ohms)

• R₀ = resistance at reference temperature (usually 25°C)

• B = thermistor’s B-value (material constant)

• T = absolute temperature in Kelvin (K)

To determine the exact resistance values across temperatures for FANUC-specific thermistors, consult the sensor’s datasheet or a standard NTC reference chart.

How to Troubleshoot and Replace the Motor Temperature Sensor

If you receive an SP9006 alarm, here’s a step-by-step process to diagnose and replace the faulty NTC thermistor:

1. Verify the Fault

• Confirm the SP9006 alarm using the CNC control’s diagnostic screen.

• Check motor temperature readings—if unavailable or abnormal, the sensor may be damaged.

2. Power Down the Equipment

• Shut down the CNC controller and disconnect power from the spindle drive system before any inspection or repair.

3. Locate the Sensor

• The temperature sensor is typically mounted on or near the spindle motor housing, often attached to the stator or rotor area.

4. Remove the Faulty Sensor

• If soldered, use appropriate soldering tools to detach the sensor from the circuit board or wiring harness.

• Handle with care to avoid damaging nearby components.

5. Install the New NTC Thermistor

• Use a replacement sensor with the exact resistance rating (typically 40kΩ at 25°C for FANUC).

• Solder the new sensor in place and ensure it maintains solid contact with the motor housing for accurate readings.

6. Test the Installation

• Before reassembly, use a multimeter to confirm resistance at room temperature.

• Power on the system and use the CNC diagnostics to verify proper sensor function and ensure the SP9006 alarm has cleared.

Additional Diagnostic Tips

• If replacing the temperature sensor doesn’t resolve the alarm, consider inspecting the spindle drive unit or the JYA2 feedback cable, which may carry the temperature signal. Faulty connections or broken internal wires in these cables can also trigger the SP9006 error.

• Do not attempt to bypass or disable the alarm. Instead, check Parameter P4134, which sets the spindle motor’s maximum temperature threshold. If the motor temperature exceeds this value, the system will automatically trigger the SP9006 alarm for protection.

Final Thoughts on FANUC SP9006 Alarms

When dealing with an SP9006 alarm in a FANUC system, replacing the temperature sensor is often the most effective fix—provided the new thermistor matches the original part’s specifications.

Key reminders:

• Always prioritize safety by disconnecting power before repairs.

• Use verified, high-quality replacement components.

• Confirm installation success using built-in diagnostic tools.

If you're unsure about the repair process, or if the alarm persists after replacing the sensor, it's advisable to consult FANUC technical support or a qualified CNC repair technician.

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