Canon MF3110 - ImageCLASS Laser Multifunction Service Manual

Also see for imageCLASS MF3111: Software guide Basic guide Specification

Contents

Chapter 2᤹ Running H/F 52-102.5.2 Protective Function2.5.2.1 Protective Mechanisms 0002-8628The machine is equipped with the following 3 types of protective mechanisms used to prevent its fixing heater fromgoing awry.1. protective mechanism by the CPU2. protective mechanism by the fixing heater safety circuit3. protective mechanism by the thermal fuse1. Protective Mechanism by the CPUThe machine's CPU monitors the voltage of the fixing heater temperature detection signal from the mainthermistor and the sub thermistor at all times, and it cuts the power to the fixing heater if it finds that the fixingtemperature appreciably exceeds a specific level.When the fixing temperature abnormally increases and the voltage of the fixing heater temperature detectionsignal from the main thermistor drops to about 0.775 V (equivalent of 235 deg C) or less, the CPU causes thefixing heater drive signal to go Low and turns off the photo triac coupler, thus cutting power to the fixing heater.If the temperature of the fixing heater abnormally increases and the voltage of the fixing heater temperaturedetection signal from the sub thermistor reaches about 2.779 V (equivalent of 320 deg C) or more, the CPUcauses the fixing heater drive signal to go Low and turns off the photo triac couple, thus cutting off the powerto the fixing heater.2. Protective Mechanism by the Fixing Heater Safety CircuitThe fixing heater safety circuit monitors the voltage of the fixing heater temperature detection signal from themain thermistor and the sub thermistor at all times.If the fixing temperature appreciably exceeds a specific level, the machine cuts off the power to the fixing heaterregardless of the instructions from the CPU.When the temperature of the fixing heater increases abnormally and the voltage of the fixing heater temperaturedetection signal of the main thermistor reaches about 0.775 V (equivalent of 235 deg C) or less, the output ofthe comparator turns Low to turn off the relay, thus cutting off the power to the fixing heater.Likewise, if the temperature of the fixing heater increases abnormally and the voltage of the fixing heatertemperature detection signal of the sub thermistor reaches about 2.779 V (equivalent of 320 deg C) or more, theoutput of the comparator turns Low to turn off the transistor, thus turning off the relay and cutting off the powerto the fixing heater regardless of the relay drive signal from the CPU.3. Protective Mechanism by the Thermal FuseIf the temperature of the fixing heater increases abnormally and the temperature of the thermal fuse exceedsabout 228 deg C, the thermal fuse starts to melt to cut off the power to the fixing heater.