Overheating Warning
Internal temperature sensors in servo amplifiers, spindle drives, or main CPU cabinet detect excessive heat levels beyond safe operating parameters (typically >85°C). This thermal protection prevents component damage by triggering warning alarms and potentially reducing system performance or initiating emergency shutdown sequences.
Error Code
E7858
Severity
Fault
Equipment
CNC Controller
Manufacturer
Bosch Rexroth
Amber or red overtemperature LED illuminated on servo amplifier front panel
HMI displays temperature alarm code (typically ALM-310 or similar) with affected module identification
Cooling fan operation at maximum speed with abnormal noise levels
Servo motor torque reduction or velocity limiting during operation
Intermittent axis positioning errors or reduced accuracy during extended machining cycles
Cabinet internal temperature reading >80°C measured at air intake sensors
Blocked air intake filters reducing airflow by >40% causing inadequate cooling capacity
Cooling fan bearing failure or blade damage resulting in insufficient air circulation
Ambient temperature elevation above 40°C exceeding equipment design specifications
Servo amplifier heat sink contamination with metal chips or coolant residue blocking thermal dissipation
Power supply internal capacitor degradation causing excessive heat generation under load
Thermal interface material degradation between CPU and heat sink reducing heat transfer efficiency
Implement LOTO procedures and disconnect all electrical power sources to CNC system
Remove and clean air intake filters using compressed air or replace if damaged beyond cleaning
Inspect cooling fans for proper rotation and replace any units showing bearing wear or blade damage
Clean heat sinks using isopropyl alcohol and soft brush to remove contamination buildup
Measure ambient cabinet temperature and install additional ventilation if readings exceed 35°C
Apply new thermal interface compound between CPU and heat sink assemblies
Restore power and verify temperature readings remain below 75°C under normal operating load
Safety First: Always isolate power and follow LOTO (Lockout/Tagout) procedures before working on electrical components. If unsure, contact a certified repair technician.
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