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Check DIAGNOSIS screen > SPM (Spindle) > scroll to thermal sensor status. Look for temperature value or thermistor resistance reading if displayed. Normal range is typically 100-500 ohms at room temperature.

Inspect spindle motor cooling fan operation. Verify fan is rotating freely and air flow is unobstructed. Check fan power supply voltage at amplifier CN (typically 200VAC or 24VDC depending on model). Replace fan if rotation is slow or noisy.

Ensure machine power is OFF and LOTO procedures followed before inspecting electrical connections.

If spindle uses through-spindle coolant or oil mist cooling, verify coolant flow and pressure. Check coolant pump operation, filter condition, and coolant lines for blockages. Clean or replace coolant filters as needed.

Allow spindle to cool completely (30-60 minutes minimum). Reset alarm and monitor spindle motor case temperature with infrared thermometer during normal operation. Compare to manufacturer specification (typically 70-90°C maximum).

Navigate to DIAGNOSIS > SPM and monitor spindle load meter during operation (typically displays as percentage). Check parameters 4000-4009 series for spindle motor specifications and verify current load does not consistently exceed 80% rated capacity.

Review CNC program for excessive duty cycle. Check spindle S-code commands and dwell times (G04). Verify adequate cooldown periods between heavy cuts. Consider reducing feed rate (F), depth of cut, or spindle speed (S) in program.

Perform spindle vibration and bearing noise test. Run spindle at various speeds (20%, 50%, 100%) without load and listen for bearing noise or unusual vibration. Check parameter 3741 (spindle orientation) and 3735 (spindle alarm detection) settings for proper configuration.

Excessive vibration or grinding noise indicates bearing failure requiring immediate spindle maintenance.

Verify spindle gear ratio and motor specifications match machine configuration. Check parameters 3741 (max spindle speed), 4001-4004 (spindle motor specs), and 4020-4025 (gear ratio parameters). Incorrect settings can cause motor overload.

Measure thermistor resistance at spindle motor terminal box. Disconnect thermistor leads (typically TH1/TH2 or red/white wires) and measure resistance with motor at room temperature. Should read 100-500 ohms for PTC thermistor, or temperature-dependent value for NTC type. Compare to spindle motor nameplate specifications.

Ensure spindle amplifier power is OFF before disconnecting thermistor to prevent damage to detection circuit.

Check spindle amplifier LED indicators. SPM series typically shows red LED for overheat condition (varies by model: αiSP-15/22/30/40). Consult amplifier manual for specific LED diagnostic codes. Verify thermistor input circuit at amplifier connector (typically JA7 or JD7).

Temporarily bypass thermal protection for testing only: Set parameter 3710 bit 0 (SP thermistor alarm disable) to 1. Run spindle briefly and monitor actual motor temperature. If alarm does not recur and temperature remains normal, thermistor or amplifier circuit is faulty.

Bypassing thermal protection removes critical safety feature. Use only for diagnostic purposes with constant temperature monitoring. Restore parameter immediately after test.