Canon 1000 Service Manual page 159

The current to the LED is controlled so that the direct intensity (level of REF-S-K) is constant, thereby
maintaining the intensity of the LED at a specific value.
DC controller PCB
Toner
supply signal
When the developer has been replaced upon installation or a sensor has been replaced, set the initial
values for the reflected light and the direct light in service mode. (See chapter 7. Troubleshooting Image
Problems.) Then, the following takes place after a copying run:
Initial values are set for the reflected light
and the direct light.
After copying operation, post rotation starts.
The transfer belt lowers.
A density pattern is formed
on the photosensitive drum.
The direct light signal and
the reflected light signal are read.
The light reflected by the
surface of the drum is read .
The toner density is
measured.
COPYRIGHT © 2001 CANON INC.
CPU
Q1
Performed when replacing the developer or sensors.
During copying operation, the density is measured
with reference to video signals.
To prevent disrupting toner images.
LED turns ON.
CANON CLC1000/1000S/3100 REV.2 MAY 2001 PRINTED IN JAPAN (IMPRIME AU JAPON)
REF-S-K
Toner density signal
LEDON*
SGNL-S-K
Figure 3-544
Corrects for dirt on the window.
Computed based on the difference between
the reflected light and the initial value.
Various measurement data units may be checked
in service mode.
Figure 3-545
3. OPERATION AND TIMING
Detection of
direct light
LED
Photosensitive
drum
Detection of
reflected light
3-115