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4.
Controlling
Grid Bias Voltage
a.
During
scanning,
the DC controller
PCB outputs GRDUFI = "0".
LQ7 goes ON and the comparator
output is 'L'.
1 Q6 goes OFF.
L Current does not flow into trans-
former T4 and 05 goes ON.
LBias
is applied to the grid.
1 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.
b.
When scanning is not taking place, the
DC controller
PCB outputs
GRDON
=
'1'.
1 Q7 gee's OFF and comparator
circuit
output is 'H'.
L Q6 goes ON and current flows into
T4.
1. Bras IS not applied to the grid.
Under
the
above
conditions,
the
surface of the drum is not charged,
hence
toner does not adhere to it (blanking).
The
timino
at which
the arid
bias
I
is switched maybe
varied using 'C&f
'
or in
'X6'
the service mode (leading edge non-
image width adjustment).
E. Controlling
Developing
Bias
,,___
1.
Outline
The
circuit
shown
in Figure
3-25
'-
controls
the developing
bias.
Its main
functions are as follows.
a.'
Switching
AC
component
of
the
developing
bias ON/OFF.
b.
Regulating
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.
a.
Settings
of COPY DENSITY
lever and
recalibration
dial
b.
AE sensor output
c.
Type of developing
assembly
When
there
is a black
developing
*-
assembly
in the copier, J306-1 and J306-4
are connected
electrically
to inform
the
copier that a black developing
assembly
is
in place.
The photosensitive
drum
gradually
deteriorates
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 copy density
lever. To
compensate
for this, operate
the COPY
DENSITY
knob,
which
can be turned
to
raise the DC bias by exactly the increase in
VL, thereby producing clear copies again.
2.
Operation
a. Switching
AC
component
of
the
\
developing
bias ON/OFF
The square
wave generator
operates
continuously
while the copier remains ON.
a)
,When ACBON = 1
LAC bias switch circuit goes ON
1 Output from the square wave
generator
is cut off.
So AC bias
is not supplied
to the
developing
cylinder.
. ..-
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