What causes FANUC alarm SV0407?

Mechanical binding or collision - axis physically obstructed by chips, crash damage, worn ways, seized ballscrew nut, or loose gibs preventing smooth motion. Inadequate servo gain settings - parameters 1825 (Position Loop Gain), 2021-2023 (Velocity Loop Gains), or 2040-2043 (Current Loop Gains) set too low for machine mass/friction, often after parameter restoration or amplifier replacement. Servo amplifier issues - alpha/beta series amplifier faults, degraded power supply voltage, blown regenerative resistor causing voltage spike protection, or loose CN1/CN2 encoder feedback cables. Overloaded or underpowered axis - commanded rapid traverse rates exceeding motor torque capacity, cutting forces too high, counterbalance pressure incorrect (Z-axis), or motor thermal overload reducing available torque. Encoder feedback failure - damaged pulse coder (encoder), contaminated scale on linear motor systems, excessive electrical noise on encoder signals, or misalignment causing AB phase signal errors detectable in parameter 1815 settings. Excessive position error limit setting - parameter 1826 set too tight for actual machine performance capabilities, particularly after maintenance work or in older machines with increased backlash.

How do I fix FANUC alarm SV0407?

1. Step 1: Check DIAGNOSIS screen (System > Diagnosis > Servo) - note which axis alarmed and review parameter 0300 (Servo Axis Number) to confirm. Check current position error value in diagnosis screen 200-207 (Position Deviation). If error is near parameter 1826 value, alarm threshold may be appropriate but actual error is problem. 2. Step 2: Manually verify axis movement - in JOG mode with feedrate override at 10%, carefully attempt to move alarmed axis in both directions. Listen for unusual noises, grinding, or binding. Check for chip accumulation, loose way covers, coolant hoses restricting travel, or visible collision damage. If axis will not move smoothly, resolve mechanical issue before proceeding. 3. Step 3: Review alarm history and velocity/current data - check ALARM screen for preceding alarms (particularly SV0401 fan alarm, SV0410 overload, or PS0101 parameter errors). Navigate to Diagnosis > Servo and monitor screens 210-217 (Velocity Feedback) and 220-227 (Motor Current) while jogging axis at low speed. Current spikes or velocity irregularities indicate mechanical loading or motor issues. 4. Step 4: Verify servo parameters - navigate to Parameters > Servo and compare critical values: 1825 (Position Loop Gain, typical 3000-5000 for modern servos), 1826 (Position Error Limit, typical 500-2000 depending on system), 2021 (Velocity Loop Gain 1), 2084 (Rapid Traverse Rate). Cross-check against machine builder specifications or backup parameter file. If recent parameter changes occurred, restore from known-good backup. 5. Step 5: Check encoder feedback signals - navigate to Diagnosis > Servo > Encoder and verify pulse count incrementing smoothly during manual movement. Inspect encoder cable connections at motor (typically CN1) and amplifier (CN2). Check for cable damage, loose connectors, or electrical interference sources near encoder cables. Review diagnosis screen 410-417 for encoder error counters. 6. Step 6: Test with increased alarm threshold temporarily - backup current parameters, then increase parameter 1826 by 50% (e.g., from 500 to 750) and re-test axis movement. If alarm clears, root cause is either mechanical wear requiring tighter tolerances or gains need optimization. Reducing rapid rates (parameter 1420-1423) may also confirm loading issue. Restore original 1826 value before final resolution. 7. Step 7: Perform servo tuning or mechanical repair - if mechanical issues found in Step 2, repair/replace worn components (ballscrews, bearings, way lubrication). If gains inadequate, use Servo Adjustment screen (Maintenance > Servo > Adjustment) to run auto-tuning function or manually optimize parameters 1825, 2021-2023 per machine builder guidelines. For amplifier faults, check DC bus voltage at amplifier display (should be 280-320VDC for 200V class) and inspect regenerative resistor connections.

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FANUC Controller

Servo/Axis · Intermediate · 30-90 minutes

Alarm SV0407

Fanuc SV0407 - Servo alarm: n axis excess error

SV0407 occurs when the actual servo position lags behind the commanded position by more than the threshold set in parameter 1826. This excessive position error indicates the servo system cannot maintain proper tracking, typically due to mechanical binding, improper servo tuning, feedback device failure, or excessive loading on the axis. The alarm protects the machine from potential crashes by stopping motion when positional accuracy is lost.

FANUCServo/AxisIntermediate30-90 minutes

SV0407

Fanuc SV0407 - Servo alarm: n axis excess error

SERVO ALARM: n AXIS EXCESS ERROR

Root Cause Summary

SV0407 occurs when the actual servo position lags behind the commanded position by more than the threshold set in parameter 1826. This excessive position error indicates the servo system cannot maintain proper tracking, typically due to mechanical binding, improper servo tuning, feedback device failure, or excessive loading on the axis. The alarm protects the machine from potential crashes by stopping motion when positional accuracy is lost.

Safety

Before manually moving any axis, ensure machine is in EMERGENCY STOP reset condition with axis unloaded and spindle OFF - sudden motor torque during diagnostic movement could cause unexpected rapid motion if obstruction clears
Do not increase parameter 1826 beyond temporary testing - excessive position error tolerance can allow crashes or collisions if actual servo tracking degrades without alarming
When checking Z-axis or vertical axes, verify counterbalance pressure is correct before testing - loss of counterbalance with increased error limits risks uncontrolled axis drop

Causes and Fixes

1
Manually move the affected axis through its full travel range with the machine powered off and motor brake released. Feel for tight spots, binding, or unusual resistance.
Ensure all E-stops are engaged and lockout/tagout procedures are followed before manual movement.
2
Inspect ballscrews, linear guides, and coupling components for wear, damage, or contamination. Check lubrication levels and verify proper grease distribution on guide rails and ballscrew.
3
Check for crash damage, bent components, or misalignment in the mechanical drivetrain. Verify coupling alignment between motor and ballscrew.
4
If binding is found, repair or replace damaged components, re-lubricate per manufacturer specifications, and re-align couplings. Test axis movement manually before re-powering.

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