What causes FANUC alarm SV0431?

Simultaneous high-speed rapids on multiple axes exceeding converter rated capacity (check axis load meters and parameter 1825 for regenerative discharge resistance settings). Mechanical binding or collision causing one or more axes to draw excessive current during motion (ballscrew damage, crash damage, way obstruction, or inadequate lubrication). Poor ventilation or high ambient temperature in electrical cabinet causing converter thermal derating (fan failure, blocked air filters, cabinet temperature >40°C/104°F). Faulty servo amplifier (alpha/beta series) drawing excessive DC bus current or internal short condition on one or more axes sharing this converter. Incorrect parameter settings for motor/amplifier combination causing overcurrent conditions (parameters 2020-2032 motor constants, parameter 2041 current loop gains). Regenerative discharge resistor failure or inadequate braking resistor capacity during deceleration of high-inertia loads (check parameter 1825 and physical resistor bank).

How do I fix FANUC alarm SV0431?

1. Step 1: Check alarm history (DIAGNOSIS screen > ALM or System > Alarm > History) to identify which axis (n) triggered the alarm and note if alarm occurred during specific motion (rapid, cutting, or machine startup) 2. Step 2: Monitor real-time servo load on all axes using servo monitor (DIAGNOSIS > SERVO > axis selection, observe current load percentage). Execute test program with single-axis motion to isolate which axis causes overload. Normal loads should be <50% during rapids, <70% during cutting 3. Step 3: Inspect electrical cabinet for environmental issues: verify all cooling fans operational, check intake/exhaust filters for blockage, measure cabinet ambient temperature (should be <40°C). Check converter module LEDs for fault indicators and listen for abnormal sounds 4. Step 4: Manually jog each axis individually (at 10-20% feedrate override) and feel for binding, unusual resistance, or mechanical noise. Check way covers, chip buildup, ballscrew condition, and lubrication system operation. Verify no crash damage or bent components 5. Step 5: Check DC bus voltage at converter output terminals (typically 280-320VDC for alpha series, 540-565VDC for beta series) and verify balanced load across all axes. Inspect regenerative discharge resistor banks for visual damage (discoloration, burning, broken connections) 6. Step 6: Review servo parameters for affected axes: verify parameter 2020-2032 motor constants match motor nameplate, check parameter 2041 current loop gains are not excessively high, confirm parameter 1825 regenerative settings are appropriate for machine inertia 7. Step 7: If all previous checks pass, suspect internal converter or servo amplifier fault. Measure insulation resistance of servo motor windings (>10MΩ to ground with motor disconnected). Contact FANUC or replace suspect servo amplifier if isolated to single axis, or replace PSM converter module if affecting all axes

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FANUC Controller

Servo/Axis · Intermediate · 30-90 minutes

Alarm SV0431

Fanuc SV0431 - Servo alarm: n axis psm overcurrent

The FANUC SV0431 alarm (n AXIS: CNV. OVERLOAD) is typically caused by excessive current demand on the power supply converter module (PSM) due to mechanical binding, simultaneous multi-axis rapid motion, or faulty components. The most likely fix involves isolating the affected axis through load monitoring and addressing mechanical or electrical issues such as binding or parameter misconfigurations.

FANUCServo/AxisIntermediate30-90 minutes

SV0431

Fanuc SV0431 - Servo alarm: n axis psm overcurrent

SERVO ALARM: n AXIS PSM OVERCURRENT

Root Cause Summary

The FANUC SV0431 alarm (n AXIS: CNV. OVERLOAD) is typically caused by excessive current demand on the power supply converter module (PSM) due to mechanical binding, simultaneous multi-axis rapid motion, or faulty components. The most likely fix involves isolating the affected axis through load monitoring and addressing mechanical or electrical issues such as binding or parameter misconfigurations.

Safety

Disconnect and lockout main power before inspecting DC bus connections or measuring voltages above 50VDC. Capacitors in PSM and servo amplifiers retain lethal voltage for 5+ minutes after shutdown
Do not manually move axes with servo power ON - high inertia loads can cause unexpected regenerative overvoltage and component damage
If mechanical binding is suspected, do not repeatedly attempt motion as this can cause permanent servo amplifier or motor damage from sustained overcurrent

Causes and Fixes

1
Inspect Axis Motion
Manually jog each axis individually at 10-20% feedrate override. Listen for unusual noises (grinding, scraping) and feel for resistance or jerky motion.
Use a dial indicator to check for ballscrew misalignment if motion feels uneven.
Ensure servo power is OFF during manual inspection to avoid unexpected motion.
2
Check Mechanical Components
Visually inspect way covers, ballscrews, and linear guides for damage, debris, or chip buildup. Verify lubrication system is delivering oil/grease to all points.
Look for scoring marks on ballscrews or guides as evidence of past collisions.
Do not force motion if binding is severe; this risks motor damage.
3
Test Load After Correction
After clearing obstructions or lubricating, run a test program with single-axis motion and monitor servo load on the DIAGNOSIS screen. Ensure load is below 50% during rapids.
If load remains high, suspect hidden damage like a bent ballscrew requiring replacement.
Avoid repeated test runs if load exceeds 70% to prevent thermal damage.

DIY Feasiblemedium confidence

Call a technician if:

·If mechanical binding cannot be resolved or requires major disassembly (e.g., ballscrew replacement).
·If electrical faults (PSM or servo amplifier) are suspected and insulation testing or component replacement is beyond skill level.

Prevention

Regularly inspect and lubricate mechanical components to prevent binding or excessive wear.
Optimize NC programs to avoid simultaneous rapid moves on multiple axes where possible.
Maintain electrical cabinet ventilation by cleaning filters monthly and ensuring fans are operational.

Common Mistakes

Ignoring early signs of mechanical binding and continuing operation, leading to servo or motor damage.
Adjusting servo parameters without proper documentation or understanding, causing instability or further alarms.

Related Alarms

401 414 417

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