FANUC SV0602 means that the inverter section of the servo amplifier has overheated. On the applicable FANUC servo amplifier, the status display commonly shows alarm 6, while the CNC displays SV0602, often described as INV. OVERHEAT or SV RADIATOR OVERHEAT.
FANUC's official troubleshooting sequence is to confirm that the servo motor is operating at or below its continuous rating, verify the cooling capacity of the electrical cabinet, check that the ambient temperature is not excessive, confirm that the control printed-circuit board is fully seated where applicable, and replace the servo amplifier if the alarm remains.
| Alarm location | Display | Meaning |
|---|---|---|
| CNC | SV0602 / INV. OVERHEAT | The servo amplifier inverter or radiator has overheated |
| Servo amplifier | 6 | Inverter overheat alarm |
| Primary inspection areas | Load and cooling | Motor duty, cabinet cooling, ambient temperature, fans, filters, and heat sink |
| Official final action | Hardware replacement | Replace the servo amplifier if external conditions and assembly are normal |
What Does FANUC SV0602 Mean?
The servo amplifier converts DC-link power into controlled three-phase current for the servo motor. Its power semiconductor devices generate heat according to motor current, acceleration and deceleration duty, machine cycle, and surrounding temperature. The radiator, heat sink, and cooling airflow must remove that heat continuously.
SV0602 is generated when the amplifier's thermal detection system identifies excessive inverter temperature. It is an amplifier overheat alarm—not automatically a servo motor overheat alarm.
The main fault areas are:
- The servo motor or axis is being used above its continuous operating capability
- The machine cycle creates excessive sustained current or insufficient cooling time
- Electrical-cabinet fans, filters, heat exchangers, or air conditioners are not providing adequate cooling
- The cabinet or amplifier ambient temperature is too high
- The servo amplifier radiator cooling fan is stopped, slow, obstructed, or installed incorrectly
- Heat-sink fins or airflow passages are blocked by oil, dust, chips, or other contamination
- The amplifier faceplate or control printed-circuit board is not fully seated, where applicable
- The amplifier's temperature-detection or power circuit is defective
SV0602 Is Not the Same as Servo Motor Overheat
The phrase “servo overheat” can be misleading because FANUC uses different alarms for the amplifier and the motor.
SV0602 identifies overheating in the servo amplifier inverter or radiator. A servo motor thermal alarm, such as SV0430 on applicable systems, concerns the motor or its thermal detection circuit and must be diagnosed using its own procedure.
Before replacing either component, confirm the exact CNC alarm number and the amplifier display. Do not diagnose SV0602 solely from the fact that a motor or amplifier feels warm.
Is 50°C the Correct Maximum Cabinet Temperature?
The technician's suggestion that the cabinet temperature must remain below 50°C may be a useful conservative machine-site limit, but it should not be presented as a universal FANUC specification.
For example, the FANUC αi Series Servo Amplifier Descriptions manual B-65282EN/06 specifies an operating ambient-temperature range of 0 to 55°C for the amplifier unit. Other amplifier series, optional hardware, CNC components, and machine builders may impose different or lower limits.
Therefore:
- Use the temperature limit stated for the exact amplifier and machine.
- Measure temperature at the amplifier environment, not only outside the cabinet.
- Do not treat the published ambient limit as the exact internal alarm trip temperature.
- A machine can still overheat below the maximum ambient limit if load is excessive or airflow is restricted.
Why SV0602 May Appear Only After Warm-Up
SV0602 often appears after the machine has operated for a period because heat accumulates gradually. A delayed alarm can indicate:
- A blocked filter that reduces airflow as cabinet temperature rises
- A slow or intermittent fan that appears normal when cold
- A heat exchanger or cabinet air conditioner with reduced performance
- Excessive axis duty during repeated machining cycles
- High motor current caused by mechanical binding, poor lubrication, excessive preload, or an imbalanced load
- Oil and dust deposited on the amplifier radiator
- An amplifier temperature-sensing or power component fault that changes as the unit warms
Record the time from cold start to alarm and whether opening the cabinet door or adding temporary external airflow changes the occurrence time. Such observations can support the diagnosis, but they are not permanent repairs and must not defeat machine safety or cabinet protection.
Safety Before Troubleshooting SV0602
The servo amplifier contains hazardous voltage and hot components. Inspection must be performed by qualified personnel using the applicable FANUC and machine-builder procedures.
Before touching the amplifier, fan, filter, connector, or control printed-circuit board:
- Stop the machine and isolate incoming electrical power.
- Wait for the specified DC-link discharge time.
- Confirm that the charge indicator is off and verify a safe electrical condition.
- Allow hot heat-sink and power components to cool before handling.
- Preserve cabinet interlocks, grounding, guards, and airflow partitions.
Do not continue operating the machine by repeatedly resetting SV0602. Repeated thermal trips can shorten component life and can lead to a more serious amplifier failure.
1. Confirm SV0602 and Amplifier Alarm 6
Confirm that the CNC displays SV0602 and that the associated servo amplifier displays 6. Record the alarm screen, amplifier display, CNC model, complete amplifier model and suffix, affected axis, and operating condition.
Determine when the alarm occurs:
- Immediately after power-up
- When servo ready is established
- During rapid acceleration or deceleration
- During a heavy machining operation
- After a repeatable period of continuous production
- Only on hot days or when cabinet doors and filters are dirty
- After a cooling fan, amplifier, motor, or cabinet component was replaced
Also review the alarm history for SV0601, SV0603, SV0430, fan alarms, overload alarms, or machine-builder cabinet-temperature warnings.
2. Confirm the Motor Is Used at or Below Its Continuous Rating
FANUC's first official check is whether the motor is being operated at or below its continuous rating. Excessive motor current also increases heat in the amplifier inverter.
Check for:
- A machining cycle with excessive continuous torque or insufficient dwell time
- Repeated high acceleration and deceleration
- A motor or amplifier that is undersized for a modified machine cycle
- Increased friction from damaged bearings, guideways, ball screws, gears, or seals
- Poor lubrication, incorrect gib adjustment, excessive preload, or mechanical binding
- An unbalanced vertical axis or malfunctioning counterbalance system
- A brake that does not fully release
- A recent increase in payload, fixture mass, cutting force, or rapid rate
Use FANUC diagnostic load data and the machine builder's test procedure to compare the affected axis under no-load and working conditions. If load has increased from its historical value, find the mechanical or process cause rather than merely increasing an overload-related setting.
Do not change motor or servo parameters to suppress SV0602 unless the machine builder and the applicable FANUC documentation specifically require a verified correction.
3. Inspect Electrical-Cabinet Cooling Capacity
FANUC directs technicians to confirm that the cabinet has sufficient cooling capacity and specifically identifies fans and filters as inspection points.
Check:
- Cabinet exhaust and circulation fans
- Air-inlet and outlet filters
- Heat exchangers or cabinet air-conditioning units
- Thermostats, fan relays, contactors, and protective devices
- Blocked air inlets, outlets, and internal circulation paths
- Incorrectly installed panels or partitions that disrupt designed airflow
- Hot air discharged from one amplifier directly into another unit
- Heat sources added to the cabinet after the original machine design
A fan that is rotating does not necessarily provide adequate airflow. Inspect its speed, direction, bearing condition, blade contamination, and airflow path. Replace clogged filters rather than removing them permanently, because unfiltered air can introduce conductive dust and oil mist into the cabinet.
4. Check Ambient and Cabinet Temperature
Measure temperature under the same operating conditions that produce the alarm. Take readings near the amplifier air inlet and radiator environment, and inspect for localized hot zones above power components.
Compare the measurements with:
- The environmental specification for the exact FANUC amplifier series
- The machine builder's cabinet-temperature limit
- The specifications of other heat-sensitive components installed in the same enclosure
- The cooling-equipment rating at the site's maximum seasonal temperature
If temperature is excessive, correct the cabinet cooling problem. Possible actions include servicing the heat exchanger or air conditioner, restoring fans and filters, improving the approved ventilation arrangement, removing unintended heat recirculation, and reducing external heat exposure.
Opening the electrical-cabinet door or directing a portable fan at the amplifier may change the symptom and help identify inadequate cooling, but it is not a proper long-term solution. It can defeat the cabinet's dust, moisture, and safety protection.
5. Inspect the Servo Amplifier Fan and Heat Sink
Check that the radiator or heat-sink cooling fan operates correctly. Inspect for:
- A stopped, slow, noisy, or intermittent fan
- Foreign material or cables obstructing the blades
- A loose or damaged fan connector
- Incorrect airflow direction after fan replacement
- Oil, dust, or chips on the fan and heat-sink fins
- A bent fan guard or damaged fan housing
- Blocked radiator ducts or insufficient clearance around the amplifier
If the fan has stopped or its speed-monitoring signal is abnormal, the CNC may also report SV0601. Follow the SV0601 procedure for the fan fault rather than treating every fan problem solely as SV0602.
Clean the heat sink and fan only by an approved method. Avoid driving conductive contamination deeper into the amplifier or scattering it across printed-circuit boards and terminals.
6. Check the Control Printed-Circuit Board Seating
On applicable FANUC servo amplifiers, the official SV0602 procedure includes confirming that the faceplate or control printed-circuit board is pushed fully into position.
Perform this check only after power has been isolated and the DC link has discharged. Inspect for incomplete seating, loose retaining points, damaged connectors, contamination, bent contacts, or evidence of previous service work.
Do not remove, reseat, or press a printed-circuit board while the amplifier is energized. If the exact amplifier does not use the removable assembly described by the manual, follow the procedure for that amplifier series rather than forcing the hardware.
7. Evaluate and Replace the Servo Amplifier
If motor load is within the continuous rating, cabinet cooling is adequate, ambient temperature is within specification, the fan and heat sink are normal, and the control board is correctly seated, FANUC directs replacement of the servo amplifier.
At this stage, possible internal faults include:
- Incorrect temperature sensing
- Deteriorated thermal interface or power semiconductor assembly
- Abnormal internal power loss
- A fan power or monitoring circuit fault that was not isolated externally
- Damage to the control or power circuit
Before installing another amplifier, verify:
- The complete FANUC part number and every suffix
- Amplifier series, axis configuration, and current capacity
- Compatibility with the CNC, servo motors, software, and machine configuration
- Cooling-fan and connector condition
- Cabinet airflow and temperature so the replacement unit is not exposed to the same cause
Do not select a replacement only by enclosure appearance or base part number. If a replacement is required, browse FANUC servo, spindle, and power drives or send the complete amplifier model to REACO CNC for a compatibility check.
8. Retest Under Normal Operating Load
After correcting the cooling or load problem—or installing the correct replacement amplifier—retest the machine according to the machine builder's procedure.
Confirm:
- SV0602 and amplifier alarm 6 no longer appear
- All cabinet and amplifier fans operate normally
- Filters, heat exchangers, and air conditioners provide adequate airflow and cooling
- The affected motor remains within its continuous operating capability
- Cabinet and amplifier ambient temperatures remain within the applicable specification
- The amplifier does not develop an abnormal temperature rise during the original failure cycle
- No SV0601, SV0603, motor-overheat, or overload alarm appears
Reproduce the operating condition that previously caused the alarm. A brief no-load test may not reveal a thermal problem that develops only after sustained production.
Difference Between SV0601, SV0602, SV0603, and SV0430
| CNC alarm | Typical amplifier display | FANUC description | Main distinction |
|---|---|---|---|
| SV0601 | F | Inverter radiator cooling fan stopped | The fan or its monitoring circuit is the primary detected fault |
| SV0602 | 6 | Inverter or servo-amplifier radiator overheat | Check motor duty, cabinet cooling, ambient temperature, fan, assembly, and amplifier |
| SV0603 | 8., 9., or A. on applicable multi-axis amplifiers | Inverter IPM overheat alarm | The intelligent power module detected an overheat condition on a specific inverter channel |
| SV0430 | System-dependent | Servo motor overheat | The detected overheat condition concerns the motor or its thermal circuit, not primarily the amplifier radiator |
Always diagnose the exact number and amplifier display. A stopped fan may eventually cause SV0602 or SV0603, but the alarm currently displayed determines the official starting procedure.
FANUC SV0602 Diagnostic Table
| Finding | Interpretation | Recommended action |
|---|---|---|
| CNC shows SV0602 and amplifier shows 6 | Servo amplifier inverter temperature is excessive | Record conditions and inspect load and cooling in the official order |
| Alarm occurs only after long production cycles | Heat is accumulating over time | Inspect continuous motor duty, cabinet temperature, airflow, fan speed, and heat-sink contamination |
| Axis load is higher than historical values | Mechanical or process load may be overheating the inverter | Inspect the machine mechanism and reduce the verified excessive load |
| Cabinet fan or heat exchanger is not operating | Cabinet cooling capacity is insufficient | Repair the cooling equipment and verify temperature under load |
| Filters or radiator fins are blocked | Airflow and heat transfer are restricted | Clean or replace components using the approved procedure |
| Radiator fan is stopped or slow | Amplifier heat cannot be removed normally | Diagnose the fan; follow SV0601 if that alarm is also present |
| Alarm occurs only on high-ambient-temperature days | Cooling capacity has inadequate margin | Measure temperature and restore the cabinet's specified cooling performance |
| Opening the cabinet delays the alarm | Inadequate cabinet cooling is likely | Repair the sealed cabinet cooling system; do not operate permanently with the door open |
| Load and cooling are normal but alarm remains | Internal amplifier sensing or power hardware may be defective | Confirm control-board seating, then replace or professionally test the amplifier |
Recommended Troubleshooting Order
- Confirm SV0602 on the CNC and alarm 6 on the servo amplifier.
- Record the amplifier model, affected axis, machine cycle, load condition, and time from cold start to alarm.
- Confirm that the servo motor is operating at or below its continuous rating.
- Inspect the axis for excessive friction, binding, brake drag, load changes, or abnormal duty.
- Check cabinet fans, filters, heat exchangers, air conditioners, and airflow paths.
- Measure temperature near the amplifier under the operating condition that produces the alarm.
- Compare the result with the exact FANUC and machine-builder environmental limits.
- Inspect the servo amplifier radiator fan, fan connector, airflow direction, and heat-sink cleanliness.
- With power isolated, confirm that the applicable faceplate or control printed-circuit board is fully seated.
- If load, cooling, temperature, fan, and assembly are normal but the alarm remains, replace or professionally test the servo amplifier.
- Retest the machine through the original production cycle and monitor load and temperature.
What Not to Do
- Do not repeatedly reset SV0602 and continue production without finding the heat source.
- Do not assume every SV0602 alarm is caused by a defective fan.
- Do not assume a rotating fan is producing the correct airflow or speed.
- Do not remove cabinet filters permanently to increase airflow.
- Do not operate permanently with the electrical-cabinet door open.
- Do not use 50°C as a universal FANUC limit without checking the exact equipment manual.
- Do not change servo parameters or overload settings to conceal excessive mechanical load.
- Do not replace the amplifier before checking motor duty, cabinet cooling, temperature, fan condition, and control-board seating.
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 6 and SV0602
- FANUC Servo Amplifier αi Series Descriptions, B-65282EN/06, environmental and installation conditions
- FANUC AC Servo Motor αi-B Series, Servo Amplifier αi-B Series Maintenance Manual, B-65515EN series, SV0602 and amplifier alarm 6
- FANUC AC Servo Motor βi Series, AC Spindle Motor βi Series, Servo Amplifier βi Series Maintenance Manual, B-65325 series, inverter overheat troubleshooting
- FANUC AC Servo Motor βi-B/βi Series, AC Spindle Motor βi Series, Servo Amplifier βi-B Series Maintenance Manual, B-65425 series, SV0602 alarm list and applicable procedures
Always use the manual edition that applies to the exact CNC, servo amplifier, servo motor, software, and machine.
Need Help With FANUC SV0602 Alarm?
REACO CNC provides independent testing, repair, compatibility checking, and replacement support for FANUC servo amplifiers, servo motors, and cooling components. Send us the CNC alarm screen, amplifier display, complete CNC model, exact servo amplifier model and suffix, affected axis, motor model, machine load information, and details of when the alarm occurs.
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 temperature limits, inspection steps, and replacement procedure depend on the exact CNC, servo amplifier, motor, software, and machine.
