Service manual

Chapter 8
8-2
8.2 Various Control Mechanisms
8.2.1 Controlling the Speed of the Fixing Roller
8.2.1.1 Controlling the Fixing Temperature 0006-4121
The fixing film unit has a plate-shaped fixing heater built into it for heating the fixing film.
The fixing heater is equipped with 2 thermistor: a main thermistor in the middle and a sub thermistor at the end. The
main thermistor is used to control the temperature of the fixing heater and to detect its overheating, while the sub
thermistor is used to detect an error temperature on the end of the fixing heater.
The CPU on the DC controller PCB monitors the main thermistor signal (FSRTH) and the sub thermistor signal
(SUBTH) from the thermistors for control of the fixing heater drive signal (FSRD0) and the relay drive signal
(RLYD), thus varying the supply of power to the heater and, ultimately, controlling the temperature of the fixing
heater.
F-8-3
The CPU on the DC controller PCB executes the following 4 types of fixing temperature
control:
- Start-Up Temperature Control
In response to a print command from the image processor PCB, the temperature of the fixing heater is started up to
Fixing assembly
Fixing
heater
Sub
thermistor
Main
thermistor
DC controller PCB
Power supply PCB
SUBTH
FSRTH
CPU
+3.3V
FSRDO
RLYD
+24V
Image processor PCB
Fixing heater high tempe-
rature error detection