Canon PC920 Service Manual page 111

2. Operations
When measuring the density of an original, the scanner turns on the scanning lamp, and moves
to a point 115 mm from the home position. At this time, the AE sensor reads the level of light
reflected by the area shown in Figure 4-112, and sends the AE signal (AE) to the DC controller
PCB.
In response, the DC controller PCB sends the developing DCON signal (serial communica-
tion) to the composite power supply PCB according to the level of the AE signal. The microproces-
sor (Q900) on the composite power supply PCB controls the level of the DC bias applied to the
developing cylinder based on the level of this signal.
Main motor (M1)
Scanner / lens drive
motor (M2)
Scanning lamp (LA1)
AE signal (AE)
COPYRIGHT © 1999 CANON INC.
68.8mm 23.5mm
(approx.) (approx.)
: Area read by AE sensor
Figure 4-114
Copy Start key
ON
STBY INTR AER
Figure 4-115
CANON PC800s/900s REV.0 AUG. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 4 IMAGE FORMATION SYSTEM
5.8mm
(approx.)
Middle of
original
37.7mm
(approx.)
SCFW SCRV SCFW SCRV LSTR STBY
4-17