FANUC SV0601 means that the radiator or heat-sink cooling fan on the servo amplifier inverter has stopped, or—on certain amplifier series—its speed has fallen below the monitored level. The CNC commonly displays SV0601 INV. RADIATOR FAN FAILURE, while the servo amplifier displays alarm F.
FANUC's official troubleshooting order is to inspect the fan for foreign material, confirm that the control printed-circuit board is fully seated where applicable, check the fan connector, replace the fan, and finally replace the servo amplifier if the alarm remains.
| Alarm location | Display | Meaning |
|---|---|---|
| CNC | SV0601 / INV. RADIATOR FAN FAILURE | The servo amplifier radiator cooling fan is not operating normally |
| Servo amplifier | F | The radiator or heat-sink cooling fan has stopped |
| Some αi-B amplifiers | Blinking F | The monitored cooling-fan speed has decreased |
| Official repair direction | Fan inspection and replacement | Check obstruction and connections, replace the fan, then replace the amplifier if necessary |
What Does FANUC SV0601 Mean?
The power semiconductor devices inside a servo amplifier generate heat during operation. A radiator or heat sink transfers that heat away from the inverter, while an external cooling fan moves air through the heat-sink fins. SV0601 is issued when the amplifier detects that this cooling fan is stopped or is no longer rotating at the required speed.
This is primarily a cooling-fan and fan-monitoring alarm. It is not normally caused by the servo motor encoder, motor power cable insulation, CNC program, servo parameters, or mechanical axis load.
The most likely fault areas are:
- Foreign material, oil residue, or contamination obstructing the fan blades
- A loose, partly inserted, damaged, or contaminated fan connector
- A worn, seized, slow, or electrically defective fan motor
- Incorrect fan installation or airflow direction after previous service
- A control printed-circuit board or faceplate that is not fully seated, where applicable
- A fault in the amplifier's fan power supply, speed-monitoring circuit, or control circuitry
SV0601 Refers to the Radiator Cooling Fan
FANUC amplifiers may contain more than one fan. SV0601 refers specifically to the fan that cools the inverter radiator or heat sink. It should not automatically be diagnosed as a cabinet air-conditioning fan or the smaller internal cooling fan inside the amplifier.
Before ordering a replacement, identify:
- The complete servo amplifier model and every suffix
- The amplifier series, such as αi, αi-B, βi, or βi-B
- The original fan or fan-unit part number
- The connector type, wiring, voltage, size, and airflow direction
- Whether the machine uses a single fan, a removable fan unit, or several fans on a wider amplifier
Fan arrangements differ among 60 mm, 90 mm, 150 mm, and 300 mm amplifier widths. Do not select a replacement only by fan dimensions or physical appearance.
Safety Before Inspecting the Fan
Servo amplifiers contain hazardous voltages even after the incoming power has been switched off. Fan inspection and replacement must be performed by qualified personnel using the applicable FANUC and machine-builder procedures.
Before removing a fan, connector, cover, faceplate, or control printed-circuit board:
- Stop the machine and isolate the incoming electrical power.
- Wait for the DC-link discharge time specified in the applicable manual.
- Confirm that the charge indicator is off and verify a safe electrical condition.
- Prevent the machine from being restarted while work is in progress.
- Record the amplifier model, alarm display, fan orientation, connector position, and wire routing.
Do not place fingers, tools, or cleaning materials into a fan while the machine is energized. Do not bypass fan monitoring or continue production with a failed cooling fan, because inadequate airflow can cause overheating and secondary amplifier damage.
1. Confirm SV0601 and Amplifier Alarm F
Confirm that the CNC displays SV0601 and that the relevant servo amplifier displays F. Photograph the displays before switching off the machine.
On some αi-B amplifier versions, a steady F indicates that the heat-sink fan has stopped, while a blinking F indicates that the monitored fan speed has decreased. The exact display behavior depends on the amplifier series and maintenance-manual edition, so record whether the character is steady or blinking.
Also record:
- Whether the alarm appears immediately at power-up or only after running
- Whether the fan is stopped, slow, noisy, intermittent, or difficult to start
- Whether recent fan, control-board, cabinet, or amplifier work was performed
- Whether the electrical cabinet has heavy oil mist, dust, chips, or poor ventilation
- Whether SV0602, SV0603, or another thermal alarm occurred before or after SV0601
2. Check for Foreign Material and Fan Obstruction
With power safely isolated, inspect the radiator cooling fan and its guard. Check for:
- Chips, wire fragments, labels, cable ties, or other foreign material touching the blades
- Oil residue, dust, or sticky contamination that prevents free rotation
- A bent guard or deformed fan housing rubbing against the blades
- Damaged, cracked, or missing blades
- A cable or connector lead entering the blade path
- Heat-sink contamination that severely restricts airflow
Turn the fan only by the approved inspection method described for the exact fan assembly. It should rotate freely without scraping, binding, or excessive bearing roughness. A fan that starts only when pushed, rotates slowly, or produces abnormal noise should be replaced even if temporary cleaning clears the alarm.
Clean only by the method permitted in the applicable maintenance documentation. Avoid forcing contamination deeper into the amplifier or scattering conductive dust across circuit boards and terminals.
3. Check the Fan Connector and Amplifier Assembly
Inspect the radiator-fan connector for complete insertion, correct orientation, bent or backed-out contacts, damaged locking features, corrosion, oil contamination, and broken conductors near the strain relief.
FANUC also instructs technicians to confirm that the faceplate or control printed-circuit board is pushed fully into position on amplifier designs where it is removable. Perform this check only with power isolated and according to the applicable amplifier procedure. Do not press, remove, or reseat a board while the amplifier is energized.
The diagram below shows typical fan-motor mounting screws, connector mounting screws, airflow direction, and fan locations on several amplifier widths.
FANUC servo amplifier radiator cooling fan locations and airflow direction for 60/90 mm, 150 mm, and 300 mm amplifier widths. Always follow the drawing for the exact amplifier model.
4. Verify Fan Operation
After completing the de-energized inspection and restoring all guards and connectors, power the machine according to the authorized test procedure. Observe the fan without bypassing cabinet interlocks or exposing personnel to energized components.
Confirm whether the fan:
- Starts normally when required by the amplifier
- Reaches a stable speed without hesitation
- Runs continuously rather than starting and stopping unexpectedly
- Produces normal airflow in the direction shown for the fan assembly
- Operates without bearing noise, vibration, or blade contact
A fan can rotate and still be defective. Some FANUC amplifiers monitor a speed-feedback signal, so a slow or unstable fan can generate SV0601 even when the blades appear to move.
5. Use a Known-Good Fan Only as a Controlled Test
If a new replacement is not immediately available, a qualified technician may use a confirmed good fan from an identical compatible amplifier as a diagnostic test. The donor fan must match the original specification, connector, voltage, wiring, speed-feedback arrangement, mounting design, and airflow direction.
Do not interchange fans merely because they have the same outside dimensions. An electrically incompatible fan can fail to run, rotate in the wrong direction, produce an incorrect monitoring signal, or damage the amplifier circuit.
If the alarm clears with the known-good compatible fan, the original fan is defective and should be replaced rather than returned to service.
6. Replace the Radiator Cooling Fan
If the fan is obstructed, seized, slow, noisy, physically damaged, or fails the controlled substitution test, replace the fan or complete fan unit specified for the exact amplifier.
Before installation, compare:
- The complete FANUC fan or fan-unit part number
- Rated voltage and current
- Connector keying and wire positions
- Fan dimensions and mounting points
- Speed-monitoring or alarm-output arrangement
- Airflow direction and label orientation
Follow the applicable removal procedure for the amplifier width. Depending on the design, replacement can involve releasing fan-unit lugs, removing metal-plate screws, removing connector mounting screws, or removing fan-motor mounting screws. Preserve all guards, ducts, brackets, and cable routing.
Install the replacement in the specified orientation. Reversing the fan can reduce heat-sink cooling even when the motor rotates normally. Make sure the connector is fully seated and that no wire can contact the blades.
If a replacement fan is required, browse FANUC servo, spindle, and power drives or send the complete amplifier and fan part numbers to REACO CNC for a compatibility check.
7. Replace the Servo Amplifier if SV0601 Remains
If the fan turns correctly, the connector is secure, the control board is correctly seated, and a known-good compatible fan does not clear SV0601, the fault may be inside the servo amplifier. Possible internal fault areas include the fan power supply, speed-detection input, connector circuit, or amplifier control circuitry.
FANUC's final action for alarm F is replacement of the servo amplifier. Before fitting another unit, verify:
- The complete amplifier part number and every suffix
- The amplifier series, axis capacity, and current rating
- Compatibility with the CNC, motors, software, and machine configuration
- Whether the original fan is supplied with the replacement amplifier or must be transferred
- The fan and connector condition before the replacement amplifier is energized
Do not install a replacement amplifier with a seized, incorrect, or shorted fan. A defective external fan can reproduce the alarm or damage the replacement unit.
8. Retest the Cooling System
After the correct fan or amplifier is installed, restore the machine according to the applicable procedure and confirm:
- SV0601 and amplifier alarm F no longer appear
- The radiator fan starts and reaches a stable speed
- Air moves in the specified direction through the heat sink
- No abnormal noise, vibration, or blade contact is present
- Fan wiring is secured away from moving blades and sharp edges
- Cabinet filters, vents, and heat exchangers are not obstructed
- No subsequent SV0602 or SV0603 thermal alarm occurs during the machine test
Run the machine through the machine builder's required test cycle and monitor the amplifier under normal operating load. If a different alarm appears, diagnose the number actually displayed rather than continuing to treat it as SV0601.
Difference Between SV0601, SV0444, SV0602, and SV0606
Several FANUC alarms involve cooling, but they identify different components or detection conditions.
| CNC alarm | Typical amplifier display | FANUC description | Main distinction |
|---|---|---|---|
| SV0444 | 1 on applicable αi amplifiers | Internal cooling fan stopped | Concerns the internal amplifier cooling fan rather than the radiator fan |
| SV0601 | F or blinking F, depending on series | Inverter radiator cooling fan stopped or slowed | Inspect the servo amplifier heat-sink fan, connector, and monitoring circuit |
| SV0602 | 6 on applicable αi amplifiers | Inverter overheat | Indicates excessive temperature; inspect load, cabinet cooling, ambient temperature, and amplifier |
| SV0606 | Converter/power-supply display varies by series | Converter radiator cooling fan stopped | Concerns the power-supply or converter module rather than the servo inverter fan |
Do not replace a servo-amplifier fan until the alarm number and the affected module have been confirmed.
FANUC SV0601 Diagnostic Table
| Finding | Interpretation | Recommended action |
|---|---|---|
| CNC shows SV0601 and amplifier shows F | Radiator cooling fan has stopped | Inspect obstruction, connector, fan, and amplifier assembly |
| Amplifier shows blinking F on an applicable αi-B system | Fan speed has fallen below the monitored level | Inspect contamination and bearings; replace a slow or unstable fan |
| Fan does not rotate and blades are obstructed | Foreign material or contamination is stopping the fan | Isolate power, remove the obstruction safely, inspect damage, and retest |
| Fan connector is loose or partly inserted | Fan power or monitoring signal is interrupted | Inspect contacts and reconnect it fully with power isolated |
| Fan is noisy, slow, intermittent, or difficult to start | Fan bearings or motor are deteriorating | Replace the fan with the exact compatible part |
| Compatible known-good fan clears the alarm | Original fan is defective | Install a correct replacement fan |
| Replacement fan rotates but SV0601 remains | Amplifier monitoring or control circuit may be abnormal | Confirm installation and compatibility, then replace or test the amplifier |
| Fan was installed in the wrong direction | Airflow through the heat sink is incorrect | Reinstall it in the specified airflow orientation |
| Heavy oil or dust repeatedly blocks the fan | Environmental contamination is causing recurring failure | Correct cabinet sealing, filtration, ventilation, and maintenance conditions |
Recommended Troubleshooting Order
- Confirm SV0601 on the CNC and record whether amplifier display F is steady or blinking.
- Record the complete servo amplifier and fan-unit part numbers.
- Isolate power, wait for DC-link discharge, and verify a safe condition.
- Inspect the fan for foreign material, oil, dust, blade damage, and mechanical obstruction.
- Inspect the fan connector, wiring, guard, housing, and heat-sink airflow path.
- On applicable designs, confirm that the faceplate or control printed-circuit board is fully seated.
- Restore the machine safely and observe whether the fan starts, reaches normal speed, and produces correct airflow.
- If necessary, test with an identical known-good compatible fan.
- Replace the defective radiator fan or complete fan unit.
- If the correct fan and connections are normal but SV0601 remains, replace or professionally test the servo amplifier.
- Retest the cooling system and verify that no thermal alarm appears under normal operation.
What Not to Do
- Do not continue operating the machine with a stopped or slow radiator fan.
- Do not bypass the fan alarm or speed-monitoring circuit.
- Do not insert tools or fingers into an energized fan assembly.
- Do not replace a fan solely by matching its dimensions.
- Do not reverse the fan or ignore the specified airflow direction.
- Do not spray contamination into circuit boards or use an unapproved cleaning method.
- Do not change servo parameters to clear SV0601; FANUC's procedure is a hardware inspection and replacement process.
- Do not replace the complete amplifier before checking the fan, connector, and assembly condition.
Technical References
- FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/04, Alarm Code F and cooling-fan replacement procedures
- FANUC AC Servo Motor αi-B Series, Servo Amplifier αi-B Series Maintenance Manual, B-65515EN/01, SV0601 alarm F and blinking F
- FANUC AC Servo Motor βi Series, AC Spindle Motor βi Series, Servo Amplifier βi Series Maintenance Manual, B-65325EN/01, radiator cooling-fan troubleshooting and replacement
- FANUC AC Servo Motor βi-B/βi Series, AC Spindle Motor βi Series, Servo Amplifier βi-B Series Maintenance Manual, B-65425EN/02, fan-unit replacement procedures
Always use the manual edition that applies to the exact CNC, servo amplifier, fan unit, software, and machine.
Need Help With FANUC SV0601 Alarm?
REACO CNC provides independent testing, repair, compatibility checking, and replacement support for FANUC servo amplifiers and cooling-fan units. Send us the CNC alarm screen, amplifier display, complete CNC model, exact servo amplifier model and suffix, fan part number, and a photo or video showing the fan condition.
Visit the FANUC Technical Support Center for more FANUC alarm guides, or contact REACO CNC for assistance.
Reference Source: Beijing FANUC. This article is based on FANUC technical documentation. The applicable inspection and replacement procedure depends on the exact CNC, servo amplifier, fan unit, software, and machine.
