Controlling The Scanning Lamp; Outline - Canon NP6218 Service Manual

CHAPTER 4 IMAGE FORMATION SYSTEM
C. Controlling the Scanning Lamp

1. Outline

Figure 4-104 shows the circuit that controls the scanning lamp; the circuit has the
following functions:
• turns on and off the scanning lamp.
• controls scanning lamp pre-heating operation.
• controls scanning lamp intensity.
• controls the scanning lamp heater.
The copier's scanning lamp is a fluorescent lamp.
In general, a fluorescent lamp is low in intensity immediately after power-on,
gradually increasing in intensity as time passes, without control; in particular, it takes a
long time before the intensity stabilizes in a low temperature environment.
If the ambient temperature drops below 15°C, the copier may enter and remain in
wait state before a specific intensity can be obtained. To prevent this from occurring, a
fluorescent lamp is provided for installation in low temperature environments.
To ensure that the lamp exposes an original at a stable intensity, a fluorescent lamp
adjusting sensor is used to monitor the intensity of the lamp during copying operation,
thereby controlling it to a specific value.
In addition, half pre-heating is executed between power-on and a press on the Copy
Start key so as to ensure that the lamp reaches its optimum intensity within a short
period of time after a press on the Copy Start key; thereafter, full pre-heating is
performed. (See Figure 4-105.)
(FL1)
Scanning lamp
SW2
Fluorescent lamp
heater switch
J202-1
(H2)
-2
Fluorescent lamp
heater
(TH3)
Fluorescent lamp
thermistor
J701-1
Fluores
cent lamp
-3
intensity
sensor
4-4
J205
T101
Main switch
T103
Main transformer
(T101) drive circuit
Fluorescent lamp
Q108
heater
FLTHON
control circuit
Figure 4-104
COPYRIGHT © 1997 CANON INC.
Composite power
T401
supply PCB
Fluorescent
lamp pre-
32KHzCLC
heating circuit
Fluorescent FL ON
lamp drive
MPWM
circuit
FLS
FLHTOFF*
FLTH
CANON NP6218 REV. 0 MAY 1997 PRINTED IN JAPAN (IMPRIME AU JAPON)
DC controller PCB
J211-3
FLPRHT*
Micro-
processor
(Q301)
Micro-
processor
(Q512)
J302-9
J211-9
5V
J317-1
FLTH
-2
-4
VR301
Reversal
amplifier
circuit