Canon PC980 Service Manual - Page 170

CHAPTER 6 FIXING SYSTEM 3. Controlling the Temperature Supplied to the Fixing Heater The temperature of the fixing heater is controlled by controlling the power supplied to the fixing heater, and the power to the fixing heater is controlled using a phase control method. The microprocessor on the DC controller PCB controls the timing at which the fixing heater duty signal (HEAT_PWM) is generated so that power suited to the target temperature of the fixing heater may be supplied (phase control). HEAT_PWM Power supplied to the heater Figure 6-105 4. Correcting the Variation in the Resistance of the Fixing Heater The characteristics of the flat heater used as the fixing heater vary from heater to heater because the production method. A discrepancy in resistance, if left alone, will not enable correct control of the fixing heater. The machine makes correction in relation to the selected level of resistance (from three settings), and corrects it basd on the readings obtained by the microprocessor. Caution: The level of resistance of the fixing heater is selected by an appropriate combination of the jumper wires connected to the connector of the fixing thermistor (TH1) and the delivery sensor (PS3). The best level is selected at the factory when the fixing assembly is assembled. Do not change the combination of jumper wires. 6-6 Figure 6-106 COPYRIGHT © 1999 CANON INC. CANON PC800s/900s REV.0 AUG. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)