Canon PC300 Service Manual page 47

OPERATIONS AND TIMING 5
©. Controlling Developing
Bias
1. Quiline
Both AC bias and DC bias are applied to
the developing cylinder during copying oper-
ation.
When the photosensitive drum is rotat-
ing except during development, about -400
V is applied to the developing cylinder
regardless of the settings made by the den-
sity control dial/lever, thereby preventing
adhesion of excess toner on the surface of
the photosensitive drum.
The copier controls the copy density by
varying the voitage of the DC component of
the developing bias (-120 to -560 V) based
on the following:
¢ Setting made by the density control
dialNever (manual density control).
» Output of the AE sensor (automatic
density control; PC320/325/FC230).
* Setting made by the density correction
switch (SW606; PC320/325/FC230).
The density correction switch (SW606)
on the control panel PCB allows three set-
tings by the user. Advise the user to change
the setting if the copies tend to be foggy
because of shifts in the sensitivity of the
photosensitive drum. SW606 is valid for
manual density control as well.
Figure 3-17 shows the changes in the
DC component of the developing bias
caused by the density control dial/lever in
manual density control mode; Figure 3-18,
on the other hand, shows changes in the DC
component of the developing bias caused by
different document densities in automatic
density adjustment mode (AE).
Note: :
The copier does not change the develop-
ing bias between black toner and color
toner. This is because the color toner
used by the copier is a single-component
agent, which allows the use of the same
developing bias as for the black toner for
development:
3-20 COPYRIGHT © 1994 1995 CANON INC.
cas Control Lever
1 (lighter)
ce 9
-100
-200
-500.
Developing bias DC component (V)
Figure 3-17A
Manual! Density Control (PC300/FC210)
Density Control Dial
canon? 5 1 (lighter)
-100
-200:
-300
-400.
ME2 (dark)
-500 ME1
MEO (light)
Developing bias DC component (\") Setting by density correction
switch (SW606)
Figure 3-17B
Manual Density Control (PC320/325/FC230)
q Test Chart Newspaper density
AE2 (dark)
-500: AEO (light)
(SW606)
Developing bias DC component (V)
Figure 3-18
Automatic Density Control (PC320/325/FC230)
CANON PC300320/325, FC210/230 REV.1 FEB. 1905 PRINTEDIN JAPAN (IMPRIME AU JAPON)