Canon CP660 Service Manual page 123

1. Primary Transfer Bias Generation Circuit
This circuit is controlled by three signals (Figure 4-602) generated by the DC con-
troller PCB, and generates the primary transfer DC (positive) bias and primary transfer
DC (negative) bias for application to the intermediate transfer drum.
The primary transfer DC (positive) bias drive signal turns on and off the DC (positive)
bias applied to the intermediate transfer drum. The primary transfer DC (negative) bias
drive signal, on the other hand, is used to turn on and off the DC (negative) bias applied
to the intermediate transfer drum.
The primary transfer bias level control is used to switch the levels of the primary trans-
fer DC (positive) bias. (See Note.)
DC controller
PCB
Primary transfer bias level control
Note:
The level of the primary transfer DC (positive) bias differs between mono-color print-
ing and full-color printing.
In the case of full-color printing, four color toners are deposited on the intermediate
transfer drum for primary transfer; as such, the toner with negative charges increases
for the second and subsequent colors, requiring increased transfer strength. To this
end, the copier increases the primary transfer bias DC component when it deals with
the second and subsequent colors.
COPYRIGHT © 1999 CANON INC.
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Primary transfer DC (positive)
bias drive signal
Primary transfer DC (negative)
bias drive signal
signal
Figure 4-602
CANON 660/2100 REV.0 FEB. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
CHAPTER 4 IMAGE FORMATION SYSTEM
Primary
transfer bias
generation
circuit
DC (positive)
or
DC (negative)
Intermediate
transfer drum
4-25