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Power down the machine and lock out. Visually inspect the torque sensor cable from spindle motor to amplifier for cuts, abrasion, or pinch damage.

Ensure proper LOTO procedures before accessing any electrical connections.

Check connectors at both the spindle motor junction box and amplifier end. Clean contacts with electrical contact cleaner and verify they are fully seated with retention clips engaged.

Measure cable resistance and continuity for each torque sensor wire according to spindle motor manual specifications. Typical resistance should be in the ohm to kilo-ohm range depending on sensor type.

If cable is damaged or readings are out of specification, replace the torque sensor cable with OEM specified part. Re-test after replacement.

With power off, disconnect the torque sensor cable at the motor junction box. Measure the sensor resistance directly at the motor terminals per motor specifications.

Reference the specific spindle motor manual for correct sensor resistance values and terminal locations.

Check for abnormal spindle motor bearing noise or excessive shaft runout that could indicate mechanical damage affecting the torque sensor. Manually rotate spindle if possible.

If sensor readings are out of spec or open/shorted, the spindle motor requires repair or replacement. Contact Fanuc or authorized spindle rebuild center for evaluation.

After motor repair/replacement, verify torque sensor parameters in spindle drive match new motor specifications and perform spindle orientation and calibration procedures.

After verifying cable and motor sensor are good, check for any other active alarms or LED error codes on the spindle amplifier that indicate control board issues.

Review spindle drive parameters (specific to your SP series amplifier) related to torque detection and verify they match OEM settings. Check for any recent parameter changes.

Measure DC power supply voltages on the spindle amplifier control board. Failed power supplies can cause sensor circuit malfunction. Verify +5V, +15V, -15V rails are within tolerance.

Use caution when measuring live circuits. Follow Fanuc electrical safety procedures.

If all external checks pass and voltages are correct, the amplifier control board likely requires replacement. Contact Fanuc for board exchange or amplifier replacement options.