Operations; Turning On/Off The Scanning Lamp; Detecting The Activation Of The Scanning Lamp; Controlling The Intensity Of The Scanning Lamp - Canon CLC 1120 Service Manual

B. Operations

1. Turning On/Off the Scanning Lamp

When LAON=0, the lamp regulator drive circuit and the intensity control circuit turn off,
causing the lamp to turn off.
When LAON=1, the lamp regulator drive circuit and the intensity control circuit turn on,
causing the lamp to turn on.

2. Detecting the Activation of the Scanning Lamp

When the lamp is on, the lamp activation detection circuit sends the activation detection signal
(LAON-S*) to the timer circuit and the CPU PCB (R-CPU). The timer circuit is reset on a
periodical basis so that the lamp may be kept on continuously as in A4/LTR continuous copying
operation (2-sheet retention).
3. Detecting an Error in the Activation of the Scanning Lamp
If an error keeps the scanning lamp on for about 60 sec (LAON-S*=0) when continuous
copying mode (2-sheet retention) is not selected, the timer circuit turns on the error latch circuit to
force the LAON signal to go '0', thereby turning off the lamp. At the same time, the lamp error
signal (LAERR) is sent to the CPU PCB.
As a result, the copier will indicate 'E220' on the control panel, and activate the auto shut-off
mechanism. If such has happened, remove the cause, and turn on the power switch to reset the copier.
In addition, the copier is equipped with the following hardware protective mechanisms to
protect against lamp malfunctions:
· If the internal temperature of the thermal switch exceeds 175°C, the thermal switch turns off
to cut off the power to the lamp.
· If an overcurrent flows because of a short circuit around the lamp, the fuse (FU1) will blow to
turn off the lamp regulator.
Caution:
The contact of the scanner thermal switch (TP1, TP6) is subject to damage when it turns on.
Do not use it once it has turned on.

4. Controlling the Intensity of the Scanning Lamp

The intensity of the lamp is determined by the pulse duty of the intensity adjustment signal
(LACNTL) from the CPU PCB, and the intensity control circuit inside the lamp regulator sends
pulse signal (PWM) to suit the pulse duty to the switching circuit, which in response keep turning
on and off at short intervals to control the current to the lamp and, ultimately, the intensity.
The pulse duty of the LACNTL signal is determined in response to FUNCTION>CCD>CCD-
ADJ in service mode, and it remains the same until the item is executed the next time.
Related Service Mode
FUNCTION > CCD > ADJ
COPYRIGHT © 1999 CANON INC.
Be sure to execute this item if you have replaced the standard white
plate, scanning lamp, R flash memory, CCD unit, analog processor
PCB, or CPU PCB.
CANON CLC1120/1130/1150 REV.0 MAR. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 3 EXPOSURE SYSTEM
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