Canon GP405 Service Manual page 74

CHAPTER 3 EXPOSURE SYSTEM
When the copyboard cover is brought down to about 30¡, the photointerrupter (PS2) mounted
at the rear turns on (i.e., light-blocking plate covers PS2). For 15 sec or until the Copy Start key is
pressed after PS2 has turned on, the output level of each sensor is read at 0.1-sec intervals. The
machine will identify the presence of an original at the sensor if its output level remains the same,
and will then identify the size of the original according to specific combinations of sensor states
(Tables 3-301, -202). This way of identification enables the use of dark originals.
The output level of each sensor, however, will not change under the conditions a or b below; in
the case of c, A3 paper will be selected first (if the appropriate cassette is absent, the standard mode
cassette will be selected).
a. An A3 dark original is used.
b. A book original is used. (The thickness of a book prevents the copyboard cover from closing
enough, not changing the output levels of the sensors.)
c. The copyboard cover is not closed. (PS2 remains off.)
Reference:
In the case of a, b, or c, the size of the original may be identified wrongly.
Copyboard cover
PS2:OFF
3-8
Copyboard cover
Original
PS2:ON
Paper sensor 1
Figure 3-402
COPYRIGHT © 1999 CANON INC. CANON 405/335 REV.0 JAN. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
30
PS2:ON
Copyboard
glass
No change
in the level
Paper sensor 2
Change in
the level