FANUC SV0600 means that excessive current was detected in the DC link of a servo amplifier inverter. The most likely causes are a short circuit or ground fault in the motor power cable, a short circuit or ground fault in the servo motor windings, or a defective servo amplifier.
On the applicable multi-axis FANUC servo amplifiers, the amplifier display identifies the affected inverter channel as 8, 9, or A. The CNC displays SV0600, usually together with the affected axis information.
| Alarm location | Display | Meaning |
|---|---|---|
| CNC | SV0600 / INV. DC LINK OVER CURRENT | Excessive current was detected in a servo amplifier DC link |
| Servo amplifier | 8 | DC-link current alarm for the L-axis inverter channel |
| Servo amplifier | 9 | DC-link current alarm for the M-axis inverter channel |
| Servo amplifier | A | DC-link current alarm for the N-axis inverter channel |
| Official repair direction | Isolation test | Disconnect the affected motor power leads, then isolate the amplifier, cable, and motor |
What Does FANUC SV0600 Mean?
The servo amplifier converts DC-link power into controlled three-phase power for the servo motor. SV0600 is generated when the inverter detects an abnormal DC-link current condition. It is therefore an electrical power-circuit alarm, not primarily a position-feedback, encoder, CNC program, or servo-tuning alarm.
FANUC identifies three principal fault areas:
- A phase-to-phase short circuit or ground fault in the servo motor power leads
- A phase-to-phase short circuit or ground fault in the servo motor windings
- A failure inside the servo amplifier
The official troubleshooting procedure separates these areas by first disconnecting the affected motor power leads from the servo amplifier. Whether the alarm remains or disappears determines the next step.
Identify the Affected Axis Before Disconnecting Anything
On a multi-axis servo amplifier, the amplifier display identifies the inverter channel that detected the abnormal current:
| Amplifier display | Inverter channel |
|---|---|
| 8 | L axis |
| 9 | M axis |
| A | N axis |
Record both the CNC alarm and the amplifier display before switching off the machine. Also record the CNC series, complete servo amplifier model and suffix, affected machine axis, and the operating condition when the alarm occurred.
The amplifier channel letter is not always the same as the machine-axis name shown to the operator. Use the machine builder's electrical drawings and FANUC axis assignment information to confirm which motor cable belongs to the indicated L, M, or N inverter channel. Disconnecting the wrong motor lead can produce a misleading diagnosis.
Common Conditions Associated With SV0600
The alarm may appear in several ways, and the timing can help direct the inspection:
- Immediately when the servo system is enabled: suspect a severe cable ground fault, motor winding fault, or amplifier power-stage failure.
- When the affected axis begins to move or accelerates: inspect the cable, motor windings, connectors, and any section of cable that flexes with axis travel.
- Only at a particular machine position: inspect the moving cable carrier, bend points, clamps, and areas where the cable can be pinched or rubbed.
- After coolant or water entered the motor or connector: suspect reduced insulation resistance and correct the source of the liquid intrusion.
- After motor, cable, or amplifier work: verify all U, V, W, and protective-earth connections and confirm that no conductors were crossed, trapped, or damaged.
The occurrence pattern is useful evidence, but it does not replace the isolation test specified by FANUC.
Safety Before Troubleshooting SV0600
SV0600 concerns the high-energy power section of the servo system. Troubleshooting must be performed by qualified personnel using the applicable FANUC and machine-builder safety procedures.
Before touching the servo amplifier, motor power connector, or terminals:
- Stop the machine and isolate the incoming electrical power.
- Wait for the required DC-link discharge time stated in the applicable manual.
- Confirm that the charge indicator is off and verify the absence of hazardous voltage as required by the site procedure.
- Label and photograph the original U, V, W, and PE connections before removal.
- Prevent disconnected conductors from contacting each other, the cabinet, or personnel.
Do not disconnect or reconnect a servo motor power cable while the machine is energized. Do not perform an insulation-resistance test through connected servo amplifier electronics. Isolate the amplifier and motor from the cable before applying any approved insulation test.
1. Confirm SV0600 and the Amplifier Display
Confirm that the CNC alarm is SV0600 and record the amplifier display as 8, 9, or A. Do not diagnose the fault solely from a translated alarm message because several FANUC alarms concern inverter current, IPM protection, or motor current.
Check the alarm history and note:
- Whether the alarm occurs at power-up, servo enable, axis movement, acceleration, or a repeatable machine position
- Whether the machine recently experienced a crash, cable replacement, motor replacement, coolant leak, or cabinet work
- Whether another power, overcurrent, insulation, or feedback alarm occurred at the same time
- Whether the affected axis was stationary or moving
If multiple alarms are present, preserve their original order. A secondary alarm generated after the power stage shuts down should not be treated as the initiating fault without evidence.
2. Inspect the External Power Circuit
With power safely isolated, inspect the affected axis motor circuit before energizing the machine again. Check:
- The servo amplifier motor-output connector and terminals
- The motor power connector and cable gland
- U, V, W, and PE conductors for loose, crossed, burned, or damaged connections
- Cable-carrier sections for crushing, excessive bending, abrasion, and coolant contamination
- Intermediate connectors, junction boxes, and terminal blocks
- Evidence of arcing, carbon tracking, moisture, corrosion, or overheating
A visual inspection can reveal an obvious cause, but a cable or motor may still have an insulation fault that is not visible.
3. Disconnect the Affected Motor Power Leads From the Amplifier
FANUC's primary isolation step is to disconnect the affected servo motor power leads from the servo amplifier. After the leads are removed, secure and insulate them so they cannot short together or contact ground.
Following the applicable machine-builder test procedure, restore the required control condition and release the emergency stop only when it is safe to do so. Observe whether SV0600 occurs with the affected motor power leads disconnected.
This test produces two diagnostic branches:
| Test result | Interpretation | Next action |
|---|---|---|
| SV0600 remains with the motor power leads disconnected | The external motor circuit is no longer loading the output, so the servo amplifier is abnormal | Replace or professionally test the servo amplifier |
| SV0600 disappears with the motor power leads disconnected | The cable or motor may have a short circuit or ground fault; the amplifier still requires evaluation if both test normal | Test and isolate the motor power cable and servo motor |
This is the most important decision point in the official troubleshooting flow.
4. If the Alarm Remains, Replace the Servo Amplifier
If SV0600 remains after the correct motor power leads have been completely disconnected, FANUC directs replacement of the servo amplifier. This result indicates that the alarm is being generated without the external cable and motor connected to the inverter output.
Before fitting a replacement, verify:
- The complete FANUC part number and every suffix
- The amplifier series, axis configuration, and current rating
- Compatibility with the CNC, servo motors, software, and machine configuration
- Connector locations, axis assignments, and machine-specific installation requirements
Do not select a replacement only by enclosure appearance or the base part number. Preserve the original configuration and follow the machine builder's commissioning procedure. If a replacement is needed, browse FANUC servo, spindle, and power drives or send the complete amplifier model to REACO CNC for a compatibility check.
5. If the Alarm Clears, Test the Motor Power Cable
If the alarm disappears with the affected motor leads disconnected from the amplifier, keep the machine power isolated and inspect the external motor circuit. FANUC's procedure calls for checking insulation between protective earth and each phase conductor:
- PE to U
- PE to V
- PE to W
Use the test method, limits, and instrument specified for the exact FANUC motor and machine. The cable must be disconnected from sensitive electronics before an insulation-resistance test. Where the applicable procedure permits, also check for phase-to-phase faults between U-V, V-W, and W-U because FANUC lists phase-to-phase short circuits among the possible causes of SV0600.
Do not assume that a cable is good because it passes a stationary test. If the alarm occurs only at a certain axis position, test while carefully flexing the isolated cable through the suspected section, following safe cable-test practices. Intermittent faults often occur inside a cable carrier or near a connector strain relief.
6. Separate the Cable From the Servo Motor
If the combined cable-and-motor circuit has poor insulation, disconnect the motor end of the power cable. Test the cable and motor separately to determine which component is defective.
| Isolated test result | Fault location | Corrective action |
|---|---|---|
| Power cable insulation is poor | Motor power cable, connector, or intermediate connection | Repair the installation issue and replace the damaged power cable or connector as specified |
| Servo motor insulation is poor | Motor windings, internal leads, or motor connector | Replace or repair the servo motor through an approved service process |
| Cable and motor insulation are both normal | No external insulation fault has been confirmed | Recheck connectors and phase-to-phase conditions; if the official isolation test still implicates the amplifier, replace or test the amplifier |
Record the measured values and test conditions. Comparing phases and repeating the test after the cable is separated can prevent replacement of the wrong component.
7. Check the Servo Motor for Moisture or Internal Damage
If the motor has reduced insulation resistance, inspect for evidence of:
- Coolant, water, or oil entering through the shaft area, connector, cable gland, or damaged seal
- Contaminated or corroded motor connector pins
- Overheated windings or a burned odor
- Crash damage, bearing failure, or mechanical conditions that may have damaged the motor
- A damaged brake or internal lead on a motor equipped with a holding brake
Replacing a wet or damaged motor without correcting the entry path can lead to the same failure again. Find and correct the leaking coolant line, failed cover, damaged seal, unsuitable cable routing, or washdown exposure before returning the machine to production.
8. Replace the Defective Cable or Motor
If testing identifies the cable or motor as defective, replace the confirmed component with the correct part. Match the complete cable or motor specification, including connector type, length, brake configuration, feedback arrangement, and all FANUC suffixes.
Route the replacement power cable according to the machine design. Protect it from sharp edges, excessive bend radius, crushing, chips, coolant, and repeated strain. Restore the protective-earth connection exactly as specified.
After installation, verify phase connections and PE continuity before applying power. A U/V/W wiring error can create another current alarm or uncontrolled motor behavior.
9. If the External Circuit Tests Normally, Evaluate the Amplifier
FANUC's detailed procedure returns to the servo amplifier when the motor power circuit insulation is normal but SV0600 is still reproduced. This is important because an amplifier can fail only when its output stage is connected or enabled, even if the disconnected-lead test does not immediately reproduce the alarm.
Before replacement, confirm that:
- The correct axis cable was isolated
- Both cable ends and all intermediate connectors were inspected
- Cable and motor were tested separately
- Test results meet the limits in the applicable FANUC documentation
- No temporary wiring, contamination, or loose terminal remains
If those checks are complete, replace or professionally bench-test the servo amplifier.
Difference Between SV0600, SV0449, and SV0438
These alarms can all appear to involve excessive current, but they identify different detection functions.
| CNC alarm | Typical amplifier display | FANUC description | Main distinction |
|---|---|---|---|
| SV0600 | 8, 9, or A | Inverter DC-link current alarm | Isolate the amplifier from the motor power cable, then test cable and motor insulation |
| SV0449 | 8., 9., or A. | Inverter IPM alarm | The decimal point is significant; diagnose the IPM protection alarm using its own procedure |
| SV0438 | b, c, or d | Inverter motor-current alarm | Can involve motor data, wiring, load, or amplifier conditions depending on the system |
Always record the decimal point on the amplifier display. Display 8 is not the same as display 8. Misreading the display can send troubleshooting toward the wrong alarm procedure.
FANUC SV0600 Diagnostic Table
| Finding | Interpretation | Recommended action |
|---|---|---|
| CNC shows SV0600 and amplifier shows 8 | DC-link current alarm on the L-axis inverter channel | Identify the assigned machine axis and perform the motor-lead isolation test |
| CNC shows SV0600 and amplifier shows 9 | DC-link current alarm on the M-axis inverter channel | Identify the assigned machine axis and perform the motor-lead isolation test |
| CNC shows SV0600 and amplifier shows A | DC-link current alarm on the N-axis inverter channel | Identify the assigned machine axis and perform the motor-lead isolation test |
| Alarm remains with affected motor leads disconnected | Internal amplifier abnormality is indicated | Replace or professionally test the servo amplifier |
| Alarm clears with motor leads disconnected | Cable or motor fault is possible | Test PE-to-U/V/W insulation and isolate the cable from the motor |
| Cable insulation is poor | Power lead, connector, or cable route is damaged | Replace the defective cable or connector and correct the cause |
| Motor insulation is poor | Servo motor winding or internal lead is damaged or contaminated | Replace or repair the motor and correct any liquid ingress |
| Alarm occurs only at one axis position | An intermittent moving-cable fault is likely | Inspect and test the cable carrier, bend points, and strain reliefs |
| Cable and motor test normally but alarm returns | Amplifier failure remains possible | Verify the isolation results, then replace or bench-test the amplifier |
Recommended Troubleshooting Order
- Confirm SV0600 on the CNC and record amplifier display 8, 9, or A.
- Use the machine documentation to identify the corresponding machine axis and motor cable.
- Record when the alarm occurs and inspect the cable, motor connector, and amplifier output for visible damage.
- Isolate machine power, wait for DC-link discharge, and verify a safe condition.
- Disconnect and safely secure the affected motor power leads at the servo amplifier.
- Under the authorized machine test procedure, determine whether the alarm remains.
- If the alarm remains, replace or professionally test the servo amplifier.
- If the alarm clears, check PE-to-U/V/W insulation and applicable phase-to-phase conditions.
- If insulation is poor, disconnect the cable from the motor and test the cable and motor separately.
- Replace the confirmed defective cable or motor and correct damage, routing, or liquid-ingress causes.
- If the external motor circuit tests normally and the alarm returns, evaluate or replace the servo amplifier.
- Retest the repaired axis at low risk under the machine builder's procedure, then verify operation through the required speed, load, and travel range.
What Not to Do
- Do not repeatedly reset and enable an axis with a suspected ground fault or short circuit.
- Do not replace the amplifier before isolating the motor circuit unless the official disconnected-lead test identifies the amplifier.
- Do not perform a high-voltage insulation test through connected amplifier electronics.
- Do not change servo parameters to clear SV0600 without evidence of a separate parameter-related alarm.
- Do not confuse amplifier display 8 with 8., because the decimal point identifies a different alarm.
- Do not return a wet motor to service without correcting the source of the water or coolant.
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 and SV0600 alarm list
- FANUC Series 0i-MODEL D/0i Mate-MODEL D Maintenance Manual, B-64305EN/03, SV0600 alarm list
- FANUC AC Servo Motor βi-B/βi Series, AC Spindle Motor βi Series, Servo Amplifier βi-B Series Maintenance Manual, B-65425EN/02, SV0600 alarm list
- The applicable FANUC servo motor maintenance manual and machine-builder electrical documentation for insulation-test limits, discharge time, axis assignment, and replacement procedures
Always use the manual edition that applies to the exact CNC, servo amplifier, servo motor, software, and machine.
Need Help With FANUC SV0600 Alarm?
REACO CNC provides independent testing, repair, compatibility checking, and replacement support for FANUC servo amplifiers, servo motors, and motor power cables. Send us the CNC alarm screen, amplifier display, complete CNC model, exact servo amplifier model and suffix, affected axis, servo motor model, 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 testing and replacement procedure depends on the exact CNC, servo amplifier, motor, software, axis configuration, and machine.
