The Fanuc Alpha-i (αi) series drive system is built from three amplifier types that work together: the PSM (Power Supply Module), the SVM (Servo Amplifier Module) and the SPM (Spindle Amplifier Module). When a fault occurs, the alarm shows in two places — a code on the amplifier's own 7-segment LED, and a matching SV / SP alarm on the CNC screen. Reading both together is the fastest way to diagnose the fault.
Where αi Alarms Appear
- On the amplifier: a 1–2 character code on the red 7-segment display (e.g. a number, or letters like U, P, L).
- On the CNC: a servo alarm (SV…) for SVM faults, or a spindle alarm (SP…) for SPM faults. The last two digits of the SP alarm usually match the SPM AL code.
PSM — Power Supply Module Alarms
The PSM feeds the DC link that powers every servo and spindle amplifier, so a PSM fault often stops the whole drive system.
| Symptom / Code | Meaning | Common Cause & Fix |
|---|---|---|
| Overheat | Heatsink / unit overheat | Blocked airflow or failed cooling fan. Clean the heatsink and replace the PSM cooling fan. |
| Cooling fan failure | Internal fan stopped | Replace the amplifier fan; check for blockage and ambient temperature. |
| DC link low voltage | Main circuit / DC link undervoltage | Check input 3-phase supply, fuses and the precharge (magnetic contactor) circuit. |
| DC link overvoltage | Regenerative / DC link over-voltage | Regenerative discharge fault or wrong PSM rating for the load. Check the regenerative resistor and braking circuit. |
| Precharge / main circuit fault | Charging of DC link failed | Faulty precharge resistor, contactor or PSM main circuit. Repair/replace the PSM. |
| Control supply undervoltage | +24 V / control power low | Check the 24 V control supply and connector CXA wiring between modules. |
SVM — Servo Amplifier Module Alarms
SVM faults show on the CNC as SV alarms (e.g. SV0401, SV0436, SV0445/0447) together with the amplifier LED code.
| Symptom / Code | Meaning | Common Cause & Fix |
|---|---|---|
| Cooling fan failure | Internal fan stopped | Replace the SVM cooling fan; clear any blockage. |
| Overheat | Amplifier / heatsink overheat | Overload, blocked cooling or high ambient. Reduce load and restore airflow. |
| DC link overvoltage | Over-voltage on the DC link | Regenerative fault from the PSM, or rapid decel. Check PSM and braking circuit. |
| Control power undervoltage (U) | Control supply too low | Check the 24 V supply and inter-module connectors. |
| IPM alarm (overcurrent / overheat) | Power transistor (IGBT/IPM) fault | Motor short, ground fault, or failed amplifier power stage. Megger the motor and cables; repair/replace the SVM. |
| Feedback disconnect (SV0445 / SV0447) | Encoder signal lost | Inspect the feedback cable/connectors; replace a faulty encoder. |
SPM — Spindle Amplifier Module Alarms (AL-xx)
Spindle faults appear on the SPM as AL- codes and on the CNC as SP alarms. The most common ones:
| Code | Meaning | Common Cause & Fix |
|---|---|---|
| AL-01 | Spindle motor overheat | Overload, blocked motor cooling fan, or faulty motor thermal sensor. Check the spindle motor fan and load. |
| AL-02 | Excessive speed deviation | Motor cannot follow the speed command — overload, belt slip, or load too high. |
| AL-03 | DC link fuse blown | Power-circuit fuse open — check the SPM main circuit and motor for shorts. |
| AL-04 | Input power open phase | Missing input phase. Check the incoming 3-phase supply and contactor. |
| AL-07 | Overspeed | Spindle exceeded the limit — parameter or feedback (sensor) fault. |
| AL-09 | Main circuit overheat (heatsink) | Cooling fan failure or blocked heatsink. Clean and replace the fan. |
| AL-11 | DC link overvoltage | Regenerative / decel over-voltage. Check the PSM and braking circuit. |
| AL-12 | DC link overcurrent | Motor short, ground fault or failed power stage. Test the motor; repair/replace the SPM. |
| AL-24 | Serial transfer / communication error | Noise or fault on the spindle serial link. Check the optical/serial cable and grounding. |
| AL-31 | Motor lock / speed-detection error | Spindle not rotating as commanded — sensor, motor or mechanical lock. |
| AL-73 | Spindle sensor disconnected | Speed/position sensor signal lost. Check the spindle sensor and feedback cable. |
First Steps When an αi Drive Alarms
- Note both the amplifier LED code and the CNC SV/SP alarm.
- Check the PSM first — if it has an alarm, the SVM/SPM alarms may be secondary.
- Check cooling fans, DC link voltage and the 24 V control supply.
- For overcurrent/IPM alarms, megger-test the motor and cables before refitting an amplifier.
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This is a quick-reference of commonly encountered αi alarms. Amplifier LED codes vary slightly by module model — always confirm against the Fanuc αi Maintenance Manual for your exact unit.