CHAPTER 7 FIXING SYSTEMCOPYRIGHT © 2002 CANON INC. 2000 CANON iR1600/iR2000 REV.1 JAN. 20027-102.4 Protective MechanismThe machine is equipped with the following protective mechanisms used to prevent mal-function of the fixing heater:1. Thermistor High TemperatureThe ASIC and the high temperature detection circuit on the DC controller monitor thevoltage readings of the main thermistor and sub thermistor; if the main thermistor detects avoltage equivalent of the following temperature, the CPU will identify the condition as indi-cating overheating.• 220°C or higher (read by main thermistor TH101)2. Thermistor DisconnectionThe connector detection circuit on the DC controller PCB monitors the THCNCT signal,and the CPU will assume that the connector of the thermistor is disconnected if the signal is‘0’.3. Cutting Off the Power in Response to Overheating (as detected by the thermalswitch)If the internal temperature of the thermal switch (THSW101) exceeds about 230°C, thethermal switch will go OFF to cut the power to the fixing heater.4. Detecting the Activation of the Fixing HeaterThe fixing heater detection circuit on the power supply PCB causes the HEATDT* signalto go ‘0’ if the FSRDRV* signal is ‘0’ (fixing heater ON). As such, the ASIC will assumethat the fixing heater activation is faulty (triac short circuit) if the HEATDT* signal goes ‘1’.
