Canon i-SENSYS MF229dw Service Manual

22 2-242-24Technical Overview > Fixing System > Various Control Mechanisms > Protective FunctionsTechnical Overview > Fixing System > Various Control Mechanisms > Protective FunctionsVarious Control Mechanisms■ Fixing Temperature Control● Heater Temperature ControlThe heater temperature control is to keep the fixing heater in the fixing film unit to thespecified temperature.The engine controller monitors the fixing heater temperature detection signal (FSRTH) andoutputs the fixing heater drive signal (FSRD) according to the detected temperature.The fixing heater drive PCB controls the fixing heater according to this signal to keep thefixing heater temperature within the target values.(220-240V model only)FU101RL101+24VFREQSNSFSRD24VOFFFSRTHCPUEngine controllerFixing heater (H1)PressurerollerThermistor (TH1)Thermal fuse (TP1) Fixing filmLow-voltagepower supplyFrequencydetectioncircuitFixing controlRelay drivecircuitFixing heaterdrive circuitFixing heatersafety circuitThere are 11 types of target fixing temperature depending on the fixing mode.These types are according to the paper type settings and resolution settings on a driver.F-2-30■ Protective Functions● Protective Function of fixing assemblyHost machine carries the following 3 functions to prevent the fixing heater from overheating.1) Protective function by CPUCPU of engine controller monitors the thermistor (TH1) temperature consistently.When TH1 reaches approx 220 deg C, CPU determines that the fixing heater is overheatingand stops the fixing heater drive signal (FSRD) output and also turns OFF relays to shutthe power supply to fixing heater.2) Protection function by fixing heater safety circuitFixing heater safety circuit monitors the thermistor (TH1) temperature consistently.When TH1 reaches approx 235 deg C, it determines that the fixing heater is overheatingand the fixing heater safety circuit turns OFF the relay drive circuit to shut the power supplyto 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.