Canon NP6317, Service Manual

Page: 66 / 248

CHAPTER 4 IMAGE FORMATION SYSTEM
COPYRIGHT © 1999 CANON INC. CANON NP6317 REV.0 APR. 1999 PRINTED IN JAPAN (IMPRIME AU JAPON)
4-8
IV. CONTROLLING DEVELOPING BIAS
A. Outline
The circuit shown in Figure 4-402 controls the developing bias. Its main functions are as fol-
lows:
1. Switching the AC component of the developing bias ON/OFF.
2. Regulating the voltage of the DC component of the developing bias.
The copy density can be controlled by varying the voltage of the developing bias to suit the
following variables:
1. Setting of the COPY DENSITY lever and recalibration dial
2. AE sensor output
The photosensitive drum gradually deteriorates with use, causing the potential (V
L
) of light
areas of the drum to increase, causing the copy density to be incorrect for a given setting of the copy
density lever. To compensate for this, a COPY DENSITY knob, which can be turned to raise the
DC bias by exactly the increase in V
L
, and thus produce clear copies again.