Canon PC720 Service Manual - Page 61

Controlling

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OPERATIONS AND TIMINGMN 3. Turning On and Off the Scanning Lamp a. Outline When pre-activation pre-heating is over, the microprocessor (Q101) on the DC controller PCB instructs the microprocessor (Q900) on the composite power supply PCB to generate the scanning lamp on signal (FLAON*). At this time, the fluorescent lamp driver circuit operates to apply the output of the primary side of the main transformer (T101) to both ends of the scanning lamp so as to turn on the scanning lamp at a high frequency. 4. Controlling the Intensity of the Scanning Lamp a. Outline The intensity of the scanning lamp is controlled by the microprocessor (O900) on the composite power supply PCB. The intensity sensor checks the intensity of the scanning lamp and generates activation power to suit the intensity. The microprocessor, on the other hand, finds out the intensity of the scanning lamp based on the activation power to send the scanning lamp on signal (FLON") to the on control circuit. b. Intensity Lower Than the Specified Value The microprocessor increases the duty ratio of the scanning lamp on signal (FLON*) sent to the fluorescent lamp driver. The fluorescent lamp driver, in turn, increases the current flowing to the scanning lamp, thereby increasing the intensity of the scanning lamp. c. Intensity Higher Than the Specified Value The microprocessor decreases the duty ratio of the scanning lamp on signal (FLOW) sent to the fluorescent lamp driver. The fluorescent lamp driver, in turn, decreases the current flowing to the scanning lamp, thereby decreasing the intensity of the scanning lamp. COPYRIGHT © 1994 CANON INC. CANON PC720/7401150770 REY.0 AUG.1994 PRINTED IN JAPAN 0mpuit AU JAPAN) 3 - 21

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OPERATIONS
AND
TIMING
MN
3.
Turning
On
and
Off
the
Scanning
Lamp
a.
Outline
When
pre
-activation
pre
-heating
is
over,
the
microprocessor
(Q101)
on
the
DC
con-
troller
PCB
instructs
the
microprocessor
(Q900)
on
the
composite
power
supply
PCB
to
generate
the
scanning
lamp
on
signal
(FLAON*).
At
this
time,
the
fl
uorescent
lamp
driver
circuit
operates
to
apply
the
output
of
the
primary
side
of
the
main
transformer
(T101)
to
both
ends
of
the
scanning
lamp
so
as
to
turn
on
the
scanning
lamp
at
a
high
fre-
quency.
4.
Controlling
the
Intensity
of
the
Scanning
Lamp
a.
Outline
The
intensity
of
the
scanning
lamp
is
controlled
by
the
microprocessor
(O900)
on
the
composite
power
supply
PCB.
The
intensity
sensor
checks
the
intensity
of
the
scanning
lamp
and
generates
activa-
tion
power
to
suit
the
intensity.
The
micropro-
cessor,
on
the
other
hand,
finds
out
the
intensity
of
the
scanning
lamp
based
on
the
activation
power
to
send
the
scanning
lamp
on
signal
(FLON")
to
the
on
control
circuit.
b.
Intensity
Lower
Than
the
Specified
Value
The
microprocessor
increases
the
duty
ratio
of
the
scanning
lamp
on
signal
(FLON*)
sent
to
the
fluorescent
lamp
driver.
The
fluo-
rescent
lamp
driver,
in
turn,
increases
the
current
flowing
to
the
scanning
lamp,
there-
by
increasing
the
intensity
of
the
scanning
lamp.
c.
Intensity
Higher
Than
the
Specified
Value
The
microprocessor
decreases
the
duty
ratio
of
the
scanning
lamp
on
signal
(FLOW)
sent
to
the
fl
uorescent
lamp
driver.
The
fluo-
rescent
lamp
driver,
in
turn,
decreases
the
current
flowing
to
the
scanning
lamp,
there-
by
decreasing
the
intensity
of
the
scanning
lamp.
COPYRIGHT
©
1994
CANON
INC.
CANON
PC720/7401150770
REY.0
AUG.1994
PRINTED
IN
JAPAN
0mpuit
AU
JAPAN)
3
-
21