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FANUC Controller
Overheat/Thermal · Intermediate · 30-60 minutes
Fanuc Alarm 431 - Converter Unit Overheat
Alarm 431 CNV. OVERLOAD indicates thermal overload protection has triggered in the converter section of the PSM (Power Supply Module) or beta/αi series SVU (Servo Unit). This occurs when internal temperature exceeds safe operating limits due to inadequate cooling, excessive load cycling, or environmental factors. The alarm protects power conversion electronics from thermal damage.
431
Fanuc Alarm 431 - Converter Unit Overheat
CNV Overheat
Thermal protection alarm activated. The cnv overheat has exceeded safe operating temperature and requires immediate attention to prevent component damage.
Root Cause Summary
Alarm 431 CNV. OVERLOAD indicates thermal overload protection has triggered in the converter section of the PSM (Power Supply Module) or beta/αi series SVU (Servo Unit). This occurs when internal temperature exceeds safe operating limits due to inadequate cooling, excessive load cycling, or environmental factors. The alarm protects power conversion electronics from thermal damage.
Safety
- High voltage present
- Allow cooling before opening cabinet
Causes and Fixes
- 1
Power down the system and inspect all cooling fans on PSM and servo amplifier units for rotation and airflow. Check for fan LED indicators on amplifier front panel (steady green = normal, red/off = fan fault).
Allow 5 minutes after power-down for capacitor discharge before opening cabinet doors.
- 2
Remove and clean/replace air intake filters on control cabinet. Inspect exhaust vents and internal air passages for dust accumulation or obstructions. Verify minimum 100mm clearance around PSM/SVU units.
- 3
Check ambient temperature inside control cabinet using SYSTEM > DIAGNOSIS > SERVO screen and verify parameter 8901#0 (temperature monitoring enable) is set to 1. Review diagnosis numbers 400-407 for servo amplifier temperatures (should be below 55°C).
- 4
Verify cabinet ambient temperature is within specification (0-45°C for most αi/β series). Install additional ventilation or air conditioning if cabinet consistently exceeds 40°C during operation.
Call a technician if:
- ·Servo amplifier internal component failure suspected
- ·Multiple simultaneous servo alarms
- ·Alarm persists after all cooling system corrections
Prevention
- Implement monthly filter inspection schedule
- Monitor ambient temperatures during seasonal changes
- Use Servo Guide for regular load monitoring
- Maintain proper cabinet door sealing
Common Mistakes
- Operating with missing or damaged filters
- Ignoring gradual fan speed reduction
- Setting acceleration parameters too aggressively
- Blocking air intake or exhaust areas with storage
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