Canon PC980 Service Manual - Page 167

CHAPTER 6 FIXING SYSTEM B. Controlling the Fixing Temperature 1. Outline The fixing lower roller of the fixing assembly is driven by the main motor (M1). When the fixing lower roller rotates, the film of the fixing upper unit starts to rotate in conjunction. The fixing film is heated by the fixing heater (H1), which is a flat heater mounted in contact with the inner side of the film. The fixing heater is equipped with a thermistor (TH1), which sends the fixing thermistor signal (TH1) to the microprocessor (Q101) on the DC controller PCB; in response, the microprocessor controls the fixing heater duty signal (HEAT_PWM) to vary the power supplied to the heater by way of controlling the temperature of the fixing heater. Relay RL601 +5V Auxiliary RLOFF* power supply Relay drive signal +5V (Q101) Thermal fuse 2 FU2 Fixing thermistor TH1 Fixing heater H1 Timer circuit Fixing heater high temperature error detection circuit HEAT_ERR* Fixing heater error signal MicroHEAT_OFF processor Fixing heater OFF signal HEAT_PWM Fixing heater duty signal HEAT_TRG Fixing heater drive signal Composite power supply PCB C123 E0_DT + E0 detection signal DC controller PCB Figure 6-103 COPYRIGHT © 1999 CANON INC. CANON PC800s/900s REV.0 AUG. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON) 6-3