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1 4. Controlling
Grid Bias Voltage
. .
~1,
(1) During scanning, the DC controller PCB
outputs GRDON = "1".
L
07
goes OFF and the comparator
output is "H".
L
Q6 goes ON.
L
Current does not flow into trans-
rByan
:,4a;;;e;",og,"h"," ,9:,'.
L
The surface of the drum is
charged.
The voltage applied to the grid is fed
back to the comparator
which functions to
maintain the grid voltage constant.
(2) When scanning is not taking place, the
DC controller
PCB outputs GRDON
=
"0".
L
07 goes ON and comparator
circuit
output is "L".
L
06 goes OFF and current flows into
T4.
LBias
is not applied to the grid.
In the above way, the surface of the
drum is not charged, hence toner does not
adhere to it (blanking).
,/-"1,
E.
k3&TROLLING
DEVELOPING
1. Outline
The circuit shown in Figure 3-18 con-
trols the developing bias. Its main functions
are as follows.
(1) Switching
AC component
of the devel-
oping bias ON/OFF.
(2) Regulating
voltage
of the DC compo-
nent of the developing
bias.
The copy density can be controlled
by
varying the voltage of the developing
bias
to suit the following variables.
(I) Settings
of copy density
cursor and
recalibration
dial
(2) AE sensor output
(3) Type of developing
unit
When there is a black developing
unit
in the copier, J605-1
and J605-4
are con-
nected electrically to inform the copier that
a black developing unit is in place.
The photosensitive drum gradually dete-
riorates with use, causing the potential (VL)
of light areas of the drum to increase, so that
copy density
is not correct
for a given
setting
of the density control cursor. To
compensate
for this, a COPY
DENSITY
RECALIBRATION
knob, which can be turned
to raise the DC bias by exactly the increase
in VL, and thus produce clear copies again.
2. Operation
a. Switching
AC component
of the devel-
oping bias ON/OFF
The square wave
generator
operates
continuously
when the copier is switched
ON.
(1) When ACBON = 1
L
AC bras swatch circuit goes ON.
L
Output from the square wave gener-
ator is cut off.
So AC bias is not supplied to the devel-
oping cylinder.
(2) When ACBON = 0
L
The AC bias switch circuit goes OFF.
So the output of the square wave oscilla-
tor goes to the Tl drive circuit. This causes
the AC high-voltage transformer
to gener-
ate a 1 BOOVAC AC bias, which is supplied
to the developing cylinder.
Also, the output of the AC high-voltage
transformer
is rectified and supplied to the
COPVAIGHT
0 1999 CANON
INC.
CANON
HP-101511215S
RN.9 OCT. 1999 PRlNTE9
IN JAPAN
(IMPAIMf
AU JAPON)
3-
17
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