FANUC SV0605 means that the regenerative power returned by the motors was excessive over a short period. On systems using the applicable αiPSR regenerative power-supply module, the power-supply display shows alarm code 8.
FANUC Maintenance Manual B-65285EN/04 identifies two principal fault paths: the regenerative resistance is insufficient for the application, or the regenerative circuit inside the PSMR/αiPSR is abnormal. The official actions are to review the regenerative-resistor specification and replace the regenerative power-supply module if its internal regenerative circuit has failed.
| Alarm location | Display | Meaning |
|---|---|---|
| CNC | SV0605 / CNV. EX. DISCHARGE POW. | The motor regenerative power is too high |
| Regenerative power supply | 8 | Excessive short-term regenerative power |
| Applicable module | αiPSR / PSMR | Regenerative power-supply module using an external regenerative discharge resistor |
| Official repair direction | Resistor specification or PSMR | Review the regenerative resistance; replace the PSMR if the regenerative circuit is abnormal |
For surrounding servo and converter alarm numbers, see the FANUC SV Alarm Codes: Servo Amplifier, Drive, Voltage and Overheat.
What Does FANUC SV0605 Mean?
When a servo or spindle motor decelerates, the mechanical energy of the moving system can be returned electrically to the common DC link. On an αiPSR system, the regenerative discharge circuit and external regenerative resistor dissipate this returned energy as heat.
SV0605 is issued when the short-term regenerative power exceeds the permitted capacity. This can happen because the machine cycle is generating more braking energy than the selected resistor system can absorb or because the regenerative circuit is not operating correctly.
Typical operating conditions that can increase regenerative energy include:
- Repeated rapid acceleration and deceleration
- Short cycle times with little cooling time between stops
- Deceleration of a high-inertia spindle, table, turret, or axis
- A recently shortened deceleration time
- A heavier workpiece, fixture, chuck, or rotating load
- Simultaneous deceleration of several motors connected to the same DC link
These conditions are diagnostic clues. They do not prove that the cycle is incorrect, because the original system may have been designed for that duty. The alarm can also occur when a previously adequate resistor, cable, connector, or regenerative power-supply circuit has deteriorated.
SV0605 Is Associated With the αiPSR/PSMR
The αiPSR is a regenerative power-supply module designed to work with an external regenerative discharge resistor. In the B-65285EN/04 maintenance manual, Alarm Code 8 is specifically listed for the αiPSR.
Do not assume that every FANUC power-supply module uses the same resistor arrangement or alarm procedure. Record the complete module number, resistor model, machine configuration, and manual edition before selecting parts or changing the circuit.
The exact FANUC ordering number and all suffixes matter. A resistor that looks similar may have a different resistance, continuous power rating, short-time energy rating, thermal protection, or connection requirement.
Confirm the Exact Location of Alarm Code 8
The character 8 is used for different conditions on different FANUC modules. Always identify which physical module displays it and confirm the CNC alarm number.
| CNC alarm and module | Display | Meaning |
|---|---|---|
| SV0605 on αiPSR/PSMR | 8 | Excessive short-term regenerative power |
| SV0600 on servo amplifier | 8 | Inverter DC-link current alarm |
| SV0603 on servo amplifier | 8. | L-axis IPM overheat; the decimal point is significant |
| Regenerative resistor alarm | H on applicable PSMR | Regenerative resistor temperature or detection-related alarm |
Do not diagnose SV0605 from the seven-segment character alone. Record both the CNC screen and every amplifier display before switching off the machine.
Official Causes Versus Supplementary Checks
FANUC's official Alarm Code 8 procedure identifies:
- Insufficient regenerative resistance — review the regenerative-resistor specification.
- Regenerative circuit failure — replace the PSMR/αiPSR.
Checks of the acceleration/deceleration cycle, resistor wiring, cabinet temperature, cooling fan, resistor value, and thermal switch can help determine why the system reached this condition. However, these checks should not be presented as though they replace the official specification review and PSMR diagnosis.
In particular, a thermal-switch fault is more directly associated with applicable Alarm Code H procedures. If the power supply displays H rather than 8, diagnose the H alarm instead of treating it as SV0605.
Safety Before Troubleshooting
The power-supply module, DC link, and regenerative discharge resistor contain hazardous energy. The resistor can become extremely hot during operation and may remain hot after the machine is stopped.
Before inspecting or measuring the circuit:
- Stop the machine using the machine builder's procedure.
- Isolate the incoming electrical supply.
- Apply lockout/tagout where required.
- Wait the discharge time specified in the applicable FANUC manual.
- Confirm that the DC-link charge indication is off and verify a safe condition.
- Allow the regenerative resistor to cool before approaching or touching it.
- Never disconnect, connect, or measure the resistor circuit while energized unless an authorized live-test procedure specifically requires it.
Resistance, continuity, insulation, and thermal-switch tests must be carried out by qualified personnel using the exact FANUC and machine-builder instructions.
1. Confirm SV0605 and Power-Supply Alarm 8
Before changing the machine cycle or ordering parts, confirm:
- The CNC shows SV0605 or CNV. EX. DISCHARGE POW.
- The regenerative power-supply module shows 8.
- The module is an αiPSR/PSMR or another model for which the same procedure is specified.
- No separate alarm appeared first on the power supply, spindle amplifier, or servo amplifier.
Record when the alarm occurs:
- At power-on
- During rapid deceleration
- During spindle stopping
- During simultaneous axis motion
- Only after repeated cycles
- After a change to the program, acceleration time, deceleration time, tooling, fixture, or workpiece
An alarm that appears consistently during the same deceleration event strongly supports an excessive regenerative-energy condition. An alarm that appears at power-on without motion may point more strongly toward wiring, resistor detection, or power-supply hardware.
2. Review the Machine's Acceleration and Deceleration Duty
Compare the current machine cycle with the condition under which the system previously operated normally.
Check whether:
- Acceleration or deceleration time was recently shortened
- Rapid traverse or spindle speed was increased
- The number of starts and stops per minute increased
- Several axes or the spindle now decelerate simultaneously
- A heavier chuck, fixture, table load, or workpiece was installed
- Mechanical drag causes the drive to work harder during the cycle
For diagnosis, a qualified technician may test with a longer deceleration time or a reduced acceleration/deceleration frequency when this is safe and permitted by the machine builder. If the alarm disappears, calculate or confirm whether the selected αiPSR and regenerative resistor are correctly rated for the actual duty.
Do not permanently slow a safety-related stopping function or alter machine-builder settings without authorization. A test that suppresses the alarm does not by itself prove that changing the cycle is the correct permanent repair.
3. Inspect the Regenerative Discharge Resistor and Wiring
With the machine safely isolated and discharged, inspect whether the specified regenerative discharge resistor is installed and connected correctly.
Check for:
- Loose or missing connections
- Heat-discolored terminals or insulation
- Burned, cracked, or mechanically damaged resistor elements
- Damaged cable insulation
- Incorrect terminal positions
- Corrosion, coolant, oil, or conductive contamination
- Evidence that the resistor or cable was changed before the alarm began
- Adequate clearance and ventilation around the resistor assembly
Use the electrical diagram for the exact machine. The uploaded illustration shows a typical αiPSR 200-V input-series arrangement and highlights the regenerative discharge resistor connection near terminals K41/K42. It is a configuration reference, not a substitute for the wiring diagram of every αiPSR model.
The following diagram shows a typical FANUC αiPSR 200-V input-series connection, including the external regenerative discharge resistor. Use it to identify the general resistor circuit, then verify the actual terminal designations and wiring against the manual for the installed power-supply model.
Figure: Typical FANUC αiPSR 200-V input-series wiring showing the external regenerative discharge resistor connection.
4. Confirm the Resistor Specification
FANUC's official action for insufficient regenerative resistance is to review the resistor specification. This means more than checking whether a resistor is physically present.
Confirm:
- Specified resistance value
- Rated continuous power
- Permitted short-time regenerative energy
- Required resistor model or approved equivalent
- Quantity and approved series/parallel arrangement
- Cable size, terminal type, and thermal-protection requirements
- Compatibility with the complete αiPSR model and machine duty
Do not arbitrarily “add another resistor” or reduce the resistance by connecting units in parallel. An incorrect resistance can exceed the switching-device current rating, damage the regenerative circuit, overheat wiring, or create a fire risk. Any capacity change must follow the applicable FANUC design tables and machine-builder approval.
5. Measure the Resistor and Thermal Protection
After the unit is isolated, discharged, and the resistor has cooled, a qualified technician can measure the resistor according to the applicable procedure.
Compare the measured value with the specified nominal resistance and tolerance. Also inspect for open circuit, unstable readings, damaged connections, or insulation failure.
If the resistor assembly includes a thermal switch, verify its state and wiring according to the correct circuit diagram. Remember that a thermal-switch or resistor-temperature problem can produce an Alarm Code H condition on applicable PSMR systems. Diagnose the code actually displayed.
Replace the resistor assembly if it is electrically or mechanically defective. Use the exact approved specification rather than choosing a replacement only by physical size.
6. Check Cooling and Cabinet Conditions as Supporting Factors
The technician-supplied procedure recommends checking cabinet temperature and power-supply cooling fans. These are sensible supporting checks because excessive heat reduces thermal margin, but FANUC's core Alarm Code 8 procedure does not list temperature or fan failure as the two principal causes of SV0605.
Check that:
- Cabinet cooling fans and filters operate normally
- Air passages are not blocked by dust or oil
- The regenerative resistor has the required ventilation and clearance
- The power-supply cooling fan is running normally
- Cabinet temperature remains within the specification for all installed devices
If the power supply displays a dedicated cooling-fan or overtemperature alarm, follow the procedure for that alarm rather than treating it only as SV0605.
7. Evaluate the Regenerative Circuit Inside the αiPSR
If the resistor specification, wiring, resistor condition, machine duty, and cooling environment are correct but SV0605 remains, the regenerative switching or detection circuit inside the αiPSR/PSMR may be abnormal.
FANUC's stated action for a regenerative circuit failure is to replace the PSMR. Internal power-supply diagnosis and component-level repair should be performed only by qualified specialists with suitable test equipment.
Before selecting a replacement, verify:
- Complete FANUC part number and all suffixes
- Input-voltage class
- Power-supply capacity
- αiPSR/PSMR series and hardware specification
- Compatibility with the connected servo and spindle amplifiers
- Required regenerative resistor and wiring configuration
If a replacement module is required, browse FANUC servo, spindle, and power drives or send the complete power-supply and resistor models to REACO CNC for a compatibility check.
8. Retest Under the Original Operating Cycle
After correcting the wiring, resistor specification, machine duty, cooling problem, or power-supply fault, retest under controlled conditions.
Confirm that:
- SV0605 and power-supply alarm 8 no longer appear
- The power-supply module completes startup normally
- The alarm does not return during the original deceleration event
- The regenerative resistor and wiring do not show abnormal heating, odor, noise, or discoloration
- No Alarm H, cooling-fan alarm, DC-link alarm, or other converter alarm appears
- The machine performs the complete production cycle correctly
If a different alarm appears, record it and follow its own procedure.
Difference Between SV0605 and Related FANUC Alarms
| Alarm | Typical display | Main condition |
|---|---|---|
| SV0600 | 8 on a servo amplifier | Inverter DC-link current alarm |
| SV0603 | 8., 9., or A. | IPM overheat on a servo-amplifier axis channel |
| SV0605 | 8 on αiPSR/PSMR | Excessive short-term regenerative power |
| PSMR Alarm H | H | Regenerative resistor overtemperature or resistor-detection-related condition |
| SP9112 | b2 / 8 on applicable spindle system | Converter excessive regenerative power reported through the spindle alarm system |
Module location, the decimal point, and the CNC alarm number are all significant. Do not treat every display containing 8 as the same fault.
FANUC SV0605 Diagnostic Table
| Finding | Interpretation | Recommended action |
|---|---|---|
| CNC shows SV0605 and αiPSR shows 8 | Excessive short-term regenerative power is detected | Record the operating event and verify resistor specification |
| Alarm occurs during every rapid stop | Regenerative energy may exceed the selected short-time capacity | Review deceleration duty and calculate the required resistor capacity |
| Alarm began after shortening cycle time | Acceleration/deceleration frequency may now be excessive | Test an approved longer cycle and review the system rating |
| Resistor is missing or incorrectly wired | Regenerative energy cannot be dissipated correctly | Restore the specified resistor and wiring |
| Terminals are loose or heat-damaged | The resistor circuit is unreliable and unsafe | Repair wiring and replace damaged components |
| Measured resistance is outside specification | Regenerative resistor is incorrect or defective | Install the exact approved resistor assembly |
| Power supply displays H instead of 8 | A resistor-temperature or detection alarm is present | Follow the Alarm H procedure |
| Resistor and machine duty are correct but alarm remains | Internal regenerative circuit may have failed | Replace or professionally test the αiPSR/PSMR |
| Different alarm appears after repair | A separate condition is now being reported | Diagnose the new alarm independently |
Recommended Troubleshooting Order
- Confirm SV0605 on the CNC and 8 on the αiPSR/PSMR.
- Record all amplifier displays and the exact operating event that triggers the alarm.
- Record the full αiPSR and regenerative-resistor models and suffixes.
- Compare the current machine cycle, speed, load, and deceleration settings with the previous normal condition.
- Isolate power, observe the discharge time, and allow the resistor to cool.
- Inspect the regenerative resistor, terminals, cable, and wiring arrangement.
- Verify the specified resistance, power rating, short-time energy capacity, and approved configuration.
- Measure the resistor and applicable thermal-protection circuit using the correct manual.
- Check cabinet and resistor cooling as supporting conditions.
- If the specification and external circuit are correct, replace or professionally test the αiPSR/PSMR.
- Retest under the original operating cycle and diagnose any new alarm separately.
What Not to Do
- Do not touch the regenerative resistor before it has cooled.
- Do not add, remove, series-connect, or parallel-connect resistors without an approved engineering specification.
- Do not select a resistor by appearance or wattage alone.
- Do not confuse power-supply display 8 with servo-amplifier display 8 or 8.
- Do not treat a cooling-fan or Alarm H condition as SV0605 without checking the displayed code.
- Do not permanently increase stopping time if it affects a safety function.
- Do not replace the αiPSR before checking the resistor specification and external circuit.
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 8 (αiPSR) / SV0605
- FANUC AC Servo Motor αis/αi Series, AC Spindle Motor αi Series, Servo Amplifier αi Series Maintenance Manual, B-65285EN/03, Alarm Code 8 (PSMR)
- Applicable FANUC Servo Amplifier αi Series descriptions and connection manual for the installed αiPSR and regenerative discharge resistor
Always use the manual edition that applies to the exact CNC, αiPSR/PSMR, regenerative resistor, connected amplifier group, and machine.
Need Help With FANUC SV0605 Alarm?
REACO CNC provides independent testing, repair, compatibility checking, and replacement support for FANUC power-supply modules, servo amplifiers, spindle amplifiers, and regenerative discharge components. Send us the CNC alarm screen, every amplifier display, complete αiPSR model, regenerative-resistor model, wiring photographs, machine cycle 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: FANUC technical documentation. The correct resistor specification, terminal arrangement, and replacement procedure depend on the exact αiPSR model, resistor assembly, amplifier configuration, and machine.
