Canon PC720 Service Manual - Page 59

Controlling, Scanning

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OPERATIONS AND TIMING= C. Controlling the Scanning Lamp 1. Outline Figure 3-304 shows the circuit that con- trols the scanning lamp (fluorescent lamp; FL1); the circuit has the following functions: • controls pre-heating of the scanning lamp. • turns on and off the scanning lamp. • controls the intensity of the scanning lamp. The copier's scanning lamp is a fluorescent lamp. When not controlled, the fluorescent lamp tends to be dark immediately after it is turned on, glowing brighter only gradually; moreover, its intensity does not stabilize for some time if its ambient temperature is low. In consideration of these characteristics of the fluorescent lamp, the copier is equipped with an intensity sensor so that the originals may be illuminated only after the intensity of the fluorescent lamp has stabilized. The copier does not start copying operation until the intensity of the fluorescent lamp has been checked and verified that it has reached a specific value. Scanning lamp Intensity sensor PCB ""At'Ar- •- Pre-heat transformer (T401) Pre-heat voltage control circuit VR101 +5V Q101 Microprocessor Main transformer (T101) Fluorescent lamp driver Q900 FLON* icroprocessor Intensity signal FLPRHT DC controller PCB Composite power supply PCB Figure 3-304 COPYRIGHT © 1994 CANON INC. CANON PC720t740R50/770 REV.O AUG.1994 PRINTED IN JAPAN fMPRIME AU JAPAN) 3- 19

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OPERATIONS
AND
TIMING=
C.
Controlling
the
Scanning
Lamp
1.
Outline
Figure
3-304
shows
the
circuit
that
con-
trols
the
scanning
lamp
(fluorescent
lamp;
FL1);
the
circuit
has
the
following
functions:
•
controls
pre
-heating
of
the
scanning
lamp.
•
turns
on
and
off
the
scanning
lamp.
•
controls
the
intensity
of
the
scanning
lamp.
The
copier's
scanning
lamp
is
a
fluores-
cent
lamp.
Scanning
lamp
Intensity
sensor
PCB
""At'Ar
-
•
-
When
not
controlled,
the
fluorescent
lamp
tends
to
be
dark
immediately
after
it
is
turned
on,
glowing
brighter
only
gradually;
moreover,
its
intensity
does
not
stabilize
for
some
time
if
its
ambient
temperature
is
low.
In
consideration
of
these
characteristics
of
the
fluorescent
lamp,
the
copier
is
equipped
with
an
intensity
sensor
so
that
the
originals
may
be
illuminated
only
after
the
intensity
of
the
fluorescent
lamp
has
stabi-
lized.
The
copier
does
not
start
copying opera-
tion
until
the
intensity
of
the
fl
uorescent
lamp
has
been
checked
and
verified
that
it
has
reached
a
specific
value.
Pre
-heat
transformer
(T401)
VR101
+5V
Q101
Microprocessor
Pre
-heat
voltage
control
circuit
Main
transformer
(T101)
Fluorescent
lamp
driver
Q900
icroprocessor
FLON*
Intensity
signal
FLPRHT
DC
controller
PCB
Composite
power
supply
PCB
Figure
3-304
COPYRIGHT
©
1994
CANON
INC.
CANON
PC720t740R50/770
REV.O
AUG.1994
PRINTED
IN
JAPAN
fMPRIME
AU
JAPAN)
3-
19