Canon PC720 Service Manual - Page 60

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I= OPERATIONS AND TIMING 2. Controlling the Scanning Lamp for Pre-Heating Pre-heating is controlled for the follow- ing: • before the scanning lamp turns on. • while the scanning lamp remains on. a. Controlling Pre-Heating before the Scanning Lamp Turns On When the Copy Start key is pressed, the microprocessor (O101) on the DC controller PCB sends the pre-heating voltage control signal (FLPRHT) to the pre-heating voltage control circuit on the composite power supply PCB. In response, the pre-heating voltage control circuit supplies 4 Vrms (effective value) to the filament of the scanning lamp. About 3 sec later, the microprocessor on the DC controller causes the pre-heating voltage control signal (FLPRHT) to go '0', to end the pre-heating operation executed before the scanning lamp turns on. b. Controlling Pre-Heating While the Scanning Lamp Remains On While the scanning lamp remains on, the microprocessor (O900) on the composite power supply PCB sends the duty ratio of the on control signal to the microprocessor (Q101) on the DC controller PCB. In response, the microprocessor (O101) on the DC controller sends the pre-heating control signal (FLPRHT) to the pre-heating voltage control circuit to execute pre-heating control suited to the duty ratio of the on control signal for pre-heating control. Reference: Activation of the Fluorescent Lamp The fluorescent lamp repeats turning on and off in specific cycles. While it is off, voltage is applied to its filament so that it will turn on smoothly, and the period during which such a voltage is being applied is called pre-heating period. 1 cycle n Off (pre-heating) Figure 3-305 The intensity of the fluorescent lamp changes within a single cycle depending on how long the lamp remains on: • longer on time E• higher intensity • shorter on time EP lower intensity The ratio of on time within a single cycle is called duty ratio, and may be expressed by the following formula: Duty ratio- ON time 1 cycle • higher duty ratioEl.increased intensity • lower duty ratio ',decreased intensity 3 - 20 COPYRIGHT © 1994 CANON INC. CANON PC720174ORMO REV.0 AUG.1994 PRINTED IN JAPAN ompRimt All JAPON)

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I=
OPERATIONS
AND
TIMING
2.
Controlling
the
Scanning
Lamp
for
Pre
-Heating
Pre
-heating
is
controlled
for
the
follow-
ing:
•
before
the
scanning
lamp
turns
on.
•
while
the
scanning
lamp
remains
on.
a.
Controlling
Pre
-Heating
before
the
Scanning
Lamp
Turns
On
When
the
Copy
Start
key
is
pressed,
the
microprocessor
(O101)
on
the
DC
controller
PCB
sends
the
pre
-heating
voltage
control
signal
(FLPRHT)
to
the
pre
-heating
voltage
control
circuit
on
the
composite
power
sup-
ply
PCB.
In
response,
the
pre
-heating
volt-
age
control
circuit
supplies
4
Vrms
(effective
value)
to
the
filament
of
the
scanning
lamp.
About
3
sec
later,
the
microprocessor
on
the
DC
controller
causes
the
pre
-heating
voltage
control
signal
(FLPRHT)
to
go
'0',
to
end
the
pre
-heating
operation
executed
before
the
scanning
lamp
turns
on.
b.
Controlling
Pre
-Heating
While
the
Scanning
Lamp
Remains
On
While
the
scanning
lamp
remains
on,
the
microprocessor
(O900)
on
the
composite
power
supply
PCB
sends
the
duty
ratio
of
the
on
control
signal
to
the
microprocessor
(Q101)
on
the
DC
controller
PCB.
In
response,
the
microprocessor
(O101)
on
the
DC
controller
sends
the
pre
-heating
control
signal
(FLPRHT)
to
the
pre
-heating
voltage
control
circuit
to
execute
pre
-heating
control
suited
to
the
duty
ratio
of
the
on
control
sig-
nal
for
pre
-heating
control.
Reference:
Activation
of
the
Fluorescent
Lamp
The
fluorescent
lamp
repeats
turning
on
and
off
in
specific
cycles.
While
it
is
off,
voltage
is
applied
to
its
filament
so
that
it
will
turn
on
smoothly,
and
the
period
dur-
ing
which
such
a
voltage
is
being
applied
is
called
pre
-heating
period.
1
cycle
n
Off
(pre
-heating)
Figure
3-305
The
intensity
of
the
fluorescent
lamp
changes
within
a
single
cycle
depending
on
how
long
the
lamp
remains
on:
•
longer
on
time
E•
higher
intensity
•
shorter
on
time
EP
lower
intensity
The
ratio
of
on
time
within
a
single
cycle
is
called
duty
ratio,
and
may
be
expressed
by
the
following
formula:
Duty
ratio-
ON
time
1
cycle
•
higher
duty
ratio
El.
increased
intensity
•
lower
duty
ratio
',decreased
intensity
3
-
20
COPYRIGHT
©
1994
CANON
INC.
CANON
PC720174ORMO
REV.0
AUG.1994
PRINTED
IN
JAPAN
ompRimt
All
JAPON)