Drive cooling fan
Common heat-related VFD and servo-drive failure point.
Fanuc Alarm 10 Servo Alarm — What It Means
Fanuc alarm 10 means servo alarm on the X-axis — specifically, the X-axis servo drive has detected an error condition and shut down that axis. On Fanuc 0, 0i, 16, 18, and 21 series controls, alarm 10 refers to the first servo axis (typically X). The alarm is generated by the servo amplifier and reported to the CNC control. It does not specify the exact servo fault — that detail is in the servo amplifier LED display (look for a number or letter on the alpha-i or beta-i amplifier module). Reading the amplifier’s own fault code is essential to diagnosis.
Common Causes
- Servo amplifier fault — The servo amplifier on the X-axis has detected an internal fault. Check the amplifier’s LED panel for a secondary code: “8” means overcurrent, “5” means overload, “1” means high voltage, etc.
- Encoder fault — A dirty, damaged, or disconnected encoder on the X-axis motor produces feedback errors that the amplifier reports as a servo alarm.
- Motor winding fault — A shorted or open winding in the X-axis servo motor drives excessive current through the amplifier, triggering the overcurrent protection.
- E-stop condition or servo ON signal missing — If the machine’s safety circuit dropped the Servo ON signal (SRV-ON) to the amplifier, it faults out. Check the E-stop circuit and safety relays.
Step-by-Step Fix
- Read the amplifier fault code — Look at the LED display on the X-axis servo amplifier. The displayed character is the actual fault code. Consult the Fanuc Servo Amplifier Maintenance Manual for the exact meaning.
- Check E-stop and safety circuit — Confirm the machine is not in E-stop. Verify the safety relay chain is closed. The Servo ON signal must be present at the amplifier for it to enable.
- Inspect encoder cable and connections — With power off, disconnect and reseat the encoder cable at both the motor and the amplifier. Look for bent pins, moisture, or visible cable damage.
- Test motor insulation — Disconnect the motor power cable at the amplifier. Use a megohm meter to test each motor lead to chassis ground. Below 1 MΩ = motor fault.
- Reset the system — After addressing the underlying cause, press the RESET key on the CNC control. If alarm 10 clears and the X-axis homes successfully, the fault is resolved.
Parts Often Needed
| Part | Notes |
|---|---|
| Fanuc servo amplifier (alpha-i or beta-i series) | Model-specific; match axis and current rating |
| Encoder (Fanuc A860 series) | Replace if encoder fault code on amplifier LED |
| Servo motor power cable | Replace if chafed or shorted near the machine cable carrier |
Technician Tips
CNC alarms should always be diagnosed by reading the full alarm text, not just the number. Modern Fanuc, Haas, and Mazak controls provide detailed alarm descriptions — press the help key while viewing the alarm for diagnostic suggestions. The alarm history screen stores the last 50-100 alarms with timestamps; review this before clearing to identify patterns. A servo alarm (SV series on Fanuc) that appears only during rapid traverse points to a different cause than one that appears during cutting.
Prevention: Back up your CNC parameters monthly. Battery-backed memory faults are much easier to recover when you have a current parameter, ladder, offset, and macro backup. Replace control batteries on a planned maintenance schedule before voltage drops far enough to risk data loss.
Need Replacement Parts?
Before ordering, match the machine-control part to the model number, electrical rating, and failure symptom. Check current prices on Amazon - prices and availability change frequently.
When to Call a Pro
Servo amplifier internal faults and motor rewinding are beyond field service. A Fanuc-certified technician with FOCAS diagnostics tools can differentiate amplifier failure from motor failure quickly.