Canon PC740 Service Manual - Page 90

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IINIOPERATIONS AND TIMING 3. Controlling the Power Supply to the Fixing Heater The temperature of the fixing heater is controlled by controlling the power supplied to the fixing heater. The power to the fixing heater is controlled by controlling its phase. The microprocessor on the DC controller PCB controls the output timing of the fixing heater driver signal (HTRD) so that power suited to the target temperature of the fixing heater may be supplied; this is to control the phase of the power supplied to the fixing heater. HTRD 4. Correcting the Variation in the Resistance of the Fixing Heater The plane-shaped heater used as the fixing heater has production variations in its resistance that would hinder proper execution of thermal control of the fixing heater. To correct possible problems, the copier compensates for the variations in terms of seven settings of the resistance, whose values are read by a microprocessor. CaUtion: The resistance of the fixing heater is decided based on the combination of the jumper wires connected to the connector of the thermistor (TH1); see Figure 3-414. The resistance is checked and appropriate settings are made at the factory when the fixing assembly is assembled; do not rearrange the jumper wires. Supply power to the heater Figure 3-413 0 0 Figure 3-414 3 - 50 COPYRIGHT © 1994 CANON INC. CANON PC120/74017501710 REVS AUG.1994 PRINTED IN JAPAN pipmmt AU JAPONI

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IINIOPERATIONS
AND
TIMING
3.
Controlling
the
Power
Supply
to
the
Fixing
Heater
The
temperature
of
the
fixing
heater
is
controlled
by
controlling
the
power
supplied
to
the
fixing
heater.
The
power
to
the
fixing
heater
is
con-
trolled
by
controlling
its
phase.
The
microprocessor
on
the
DC
controller
PCB
controls
the
output
timing
of
the
fixing
heater
driver
signal
(HTRD)
so
that
power
suited
to
the
target
temperature
of
the
fixing
heater
may
be
supplied;
this
is
to
control
the
phase
of
the
power
supplied
to
the
fixing
heater.
HTRD
Supply
power
to
the
heater
Figure
3-413
4.
Correcting
the
Variation
in
the
Resistance
of
the
Fixing
Heater
The
plane
-shaped
heater
used
as
the
fixing
heater
has
production
variations
in
its
resistance
that
would
hinder
proper
execu-
tion
of
thermal
control
of
the
fixing
heater.
To
correct
possible
problems,
the
copier
compensates
for
the
variations
in
terms
of
seven
settings
of
the
resistance,
whose
val-
ues
are
read
by
a
microprocessor.
CaUtion:
The
resistance
of
the
fixing
heater
is
decided
based
on
the
combination
of
the
jumper
wires
connected
to
the
con-
nector
of
the
thermistor
(TH1);
see
Figure
3-414.
The
resistance
is
checked
and
appro-
priate
settings
are
made
at
the
factory
when
the
fixing
assembly
is
assem-
bled;
do
not
rearrange
the
jumper
wires.
0
0
Figure
3-414
3
-
50
COPYRIGHT
©
1994
CANON
INC.
CANON
PC120/74017501710
REVS
AUG.1994
PRINTED
IN
JAPAN
pipmmt
AU
JAPONI