Canon MF4500 Series Service Manual

Canon MF4500 Series Service Manual Manual pdf 49 page image

22 2-242-24Technical Overview > Fixing System > Various Control Mechanisms > Protective FunctionsTechnical Overview > Fixing System > Various Control Mechanisms > Protective Functionsto the fixing heater.3) Protection function by temperature fuse (TP1)When the fixing heater temperature rises abnormally and temperature fuse (TP1)temperature reaches approx 226 deg C, TP1 opens to shut the power supply to the fixingheater.● Failure detectionWith this machine, 8 types of failure detection are available.1) Initial startup failure detectionWhen temperature of the Fixing Assembly does not exceed 50 deg C within 1.48 sec afterthe start of temperature control performed at initial rotation, it is judged as initial startupfailure.2) Initial Thermistor open detectionWhen temperature of the Fixing Assembly does not exceed 35 deg C within 1.48 sec afterthe start of temperature control at warm-up rotation temperature control or at cleaningmode, it is judged as Thermistor open failure.3) Short circuit of Thermistor/abnormal high temperature detectionWhen temperature of the Fixing Assembly is 220 deg C or higher for 30 consecutive timesby monitoring the temperature for every 5 msec, it is judged as Thermistor short circuitfailure. In addition, this function also doubles as abnormal high temperature detectionfunction of the Fixing Assembly.4) Abnormal low temperature detectionAfter temperature of the Fixing Assembly exceeds 50 deg C at least once, monitortemperature of the Thermistor for every 5 msec. It is judged as heater abnormal lowtemperature when the following condition is detected 240 consecutive times: thetemperature is 100 deg C or lower while paper is at fixing nip, or it is 55 deg C or lowerduring paper interval temperature control or at cleaning mode.5) Thermistor open detectionAfter temperature of the Fixing Assembly exceeds 50 deg C, monitor temperature of theThermistor for every 5 msec. When it is detected that the temperature is lower than 20 degC for 6 consecutive times, it is judged as Thermistor open failure.6)Startup failure detectionIf temperature of the Fixing Assembly is 100 deg C or higher when the machine becomes inpickup enabled state after entering fixing low voltage inlet sequence, it is judged as startupfailure.7) Thermistor low temperature detection 2)Temperature of the Thermistor is monitored for every 200 msec when paper is at fixingnip during the Fixing Assembly control. When the temperature is lower than 135 deg C(120 deg C), increase the value of low temperature detection counter by 1 (+1). When itis 135 deg C (120 deg C) or higher, decrease the value by 1 (-1). When the value of lowtemperature counter becomes +150, it is judged as Thermistor low temperature failure. Thedefault and minimum value of low temperature detection counter is 0.8)Frequency detection circuit error (230V models only)When frequency measurement is not completed within 3255 msec after the completion ofprevious frequency measurement, it is judged as frequency detection circuit error.● Processing after failure detectionIf the Main Motor is in driving state when Fixing Assembly failure is detected, rotation of themotor is maintained for 300 msec after the machine moves in Fixing Assembly failure state.Then, drive systems (Main Motor system, Laser/Scanner system, high voltage system, andfixing system) are stopped immediately and the machine moves in failure state.If the Main Motor is not in driving state, drive systems are stopped immediately and themachine moves in failure state.