Canon PC300 Service Manual page 64

2. Controlling the Fixing Heater
Temperature
The target temperature for the fixing
heater is controlled to four settings (155°,
165°, 175°C, 185°C) by the microprocessor
based on the following conditions:
a. Temperature of the fixing heater at
power-on.
b. Temperature of the fixing heater at the
beginning of copying operation.
c. How many copies have been made.
3. Conirolling ihe Supply Power to the
Fixing Heater
The temperature of the fixing heater
(H1) is controlled by controlling the power
supplied to the fixing heater.
The power to the fixing heater is con-
trolled by a phase power control method.
The microprocessor on the DC con-
troller/DC power supply circuit takes on the
zero-cross signal (ZXDP) from the zero-
cross signal generator circuit as a sync sig-
nal to identify the AC input voltage in relation
to the reference voltage signal (VPEAK)
from the reference voltage sensor circuit.
Using the reading, the microprocessor
controls the fixing heater drive command
(HTRD) power to attain the specific target
temperature for the fixing heater, in other
words exerting phase control on the supply
power to the fixing heater.
Reference
voltage
sensor circuit
DC controller/DC power supply PCB
Figure 3-32
COPYRIGHT © 1994 CANON INC.
Microprocessor
CANON PC300320/225, FC210/290.REV.O JULY 1904 PRINTED IN JAPAN (IMPRIME AU JAPON)
PERATIONS AND TIMING
Further, 'E9' is indicated on the control
panel if the zero cross signal (ZXDP) falls
below a specific value because of an error in
the frequency of the power supply.
AC input
signal
ZXDP
signal
ee inks es aa
A
signal
HTRD
waenennenennnnnnng
Supply power
to heater
Figure 3-33
3-37