Controlling The Fixing Film Bias; Fixing Heater Safety Mechanism; Detecting A Fault In The Fixing Assembly - Canon SmartBase 1270D Service Manual

6.2.2 Controlling the Fixing Film Bias

The machine is equipped with a fixing film bias control mechanism which is controlled
by the CPU on the DC controller PCB. The fixing film bias is used to prevent displacement
of toner deposits; i.e., when the primary charging roller DC bias is applied, a bias of the
same polarity as the toner is applied to the fixing film so as to create a magnetic field be-
tween the paper and the film.
DC controller PCB
Primary charging
roller
AC bias drive circuit
CPU
Primary charging
roller
DC bias drive circuit

6.2.3 Fixing Heater Safety Mechanism

The fixing heater safety circuit is part of the DC controller PCB, and is used to monitor
the fixing temperature for an error at all times. If the output voltage for the main thermistor
or the sub thermistor reaches about 0.37 V or lower (about 310°C/590°F), the relay will be
turned off regardless of the state of the relay drive signal (RLYD) from the CPU to shut the
power to the fixing heater.
If the temperature of the fixing heater increases abnormally, on the other hand, to exceed
about 230°C/446°F, the thermal fuse will melt to cut the power to the fixing heater.

6.2.4 Detecting a Fault in the Fixing Assembly

The CPU on the DC controller PCB will identify a fault in the fixing assembly if any of
the following conditions (a through f) occurs; as a result,
• it will cut the power to the fixing heater.
• it will cause the relay drive signal (RYLD) to go '1' to turn off the relay and, at the
same time, will communicate the presence of a fault to the image processor PCB.
COPYRIGHT © 2002 CANON INC.
Superposition
F04-602-02
2000 2000 2000 2000 CANON SmartBase PC1210D/1230D/1270D REV. 1 MAR. 2002
CHAPTER 4 OPERATION
Rimary
J205
charging
roller
Photosensitive
drum
J206
Fixing film
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