An ‘F’ on a Fanuc servo amplifier's 7-segment display means a cooling fan has stopped. On the CNC screen it appears as SV0444 (n-axis: internal fan stopped) or SV0601 (n-axis: radiator/heatsink fan stopped) depending on which fan failed — αi SVM units have both: a small internal fan circulating air inside the case, and an external fan cooling the heatsink at the back of the cabinet. It looks like a trivial alarm. Treat it seriously anyway: the fan is what stands between a ₹5,000 repair and a cooked IGBT module, and Fanuc trips the alarm precisely because amplifiers routinely die of heat after fans die of dust.
Which fan is it?
- SV0444 / internal fan: the small fan inside the amplifier case (top of the unit on most SVM αi models). The amplifier usually will NOT run with this fan stopped — the alarm is immediate.
- SV0601 / radiator fan: the external fan on the heatsink that pokes through the cabinet rear. Some systems allow limited operation and escalate to an overheat alarm later; do not use that grace period for production.
- On βi SVU/SVSP units the same ‘F’ logic applies with the unit's fan(s).
Step 1 — Confirm and inspect (10 minutes)
- Power the cabinet safely and look/listen: is the fan spinning at all, spinning slowly, or twitching? A fan that starts after a finger-spin (power off first!) has worn bearings — it is dead, it just doesn't know it yet.
- Dust check: in Indian shop conditions the most common find is a fan matted solid with oil-laden dust — the motor is fine but stalled. Blow out the fan and the heatsink fins (power off, mask up) and retest. If it runs, still plan a fan replacement — a stalled-and-restarted fan has stressed windings.
- Connector: reseat the fan's small connector on the amplifier — vibration and brittle wires at the crimp are regular culprits.
Step 2 — Replace the fan (the normal fix)
- Fanuc fans are field-replaceable units: the internal fan is typically a slide-in cassette at the top of the SVM (one connector, one or two screws); the radiator fan unbolts from the heatsink duct. Note the airflow direction arrow before removal and match it on installation.
- Use the correct Fanuc fan unit for your amplifier model (the A06B-… spec is on the amplifier's nameplate/parts list) — generic fans with the wrong airflow or missing the speed-sense wire will keep the alarm on: the amplifier monitors fan rotation via a sense signal, not just power, so a two-wire generic fan reads as ‘stopped’ even while spinning.
- Power up and confirm the display clears and the fan runs at full speed.
Step 3 — If a new fan does not clear the alarm
- Fan power/sense circuit on the amplifier board: a failed fan-drive transistor or sense input keeps the alarm latched with a healthy fan — board-level repair.
- Wrong fan variant: double-check the model — same frame size, different connector pinouts exist across SVM generations.
- Check the alarm axis number: on multi-axis SVMs (2- and 3-axis modules) the F/SV0444 may point at the module, not the axis you assumed — confirm which physical unit shows ‘F’.
The bigger picture — heat is the real enemy
A stopped fan is often the visible symptom of a cabinet-cooling problem: clogged cabinet filters, a failed heat exchanger, or a cabinet door left open in summer (which pulls dusty air across everything). While you are in there: clean the filters, verify the cabinet heat exchanger/AC works, and feel the amplifier heatsinks after a heavy cycle — too hot to hold for 5 seconds means cooling is marginal even with fans running. Amplifiers that live hot die young: bus capacitors dry out (see our undervoltage guides) and IGBT modules fail (see AL-12).
Related guides
- Fanuc αi drive alarms — PSM, SVM & SPM codes explained
- Fanuc servo drive alarm codes
- CNC preventive maintenance checklist