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operations and
timing
4.
Controlling Grid
Bias Voltage
a.
During s canning, the
DC
controller
PCB
outputs
GRDON
=
"0".
I»Q7
goes
ON
and
the
comparator
output
is
"L".
L
Q6
goes OFF.
L> Current
does
not flow
into
trans-
former
T4
and
Q5
goes
ON.
'-Bias
is
applied
to
the
grid.
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.
b.
When
scanning
is
not taking place,
t
he
DC
controller
PCB
outputs
GRDON
=
"1
".
Lqj
goes
OFF
and comparator
circuit
output
is
"H".
-Q6
goes
ON
and
current flows
into
T4.
I—
Bias
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
timing
at
which
the
grid
bias
is
switched
may
be
varied using Z3'
or
T6'
in
the service
mode
(leading
edge non-image
width adjustment).
E.
Controlling
Developing
Bias
1.
Outline
The
circuit
shown
in
Figure
3-18
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
assem-
bly
in
the
copier,
J303-1
and
J303-4
are
con-
nected
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
tp
increase,
so
that
copy
density
is
not correct
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
Vl,
and
thus
produce
clear
copies
again.
2.
Operation
a.
Switching
AC
component
of
the
developing
bias
ON/OFF
The
square
wave
generator operates
continuously
when
the copier
is
switched
ON.
a)
WhenACBON
=
1
LaC
bias switch
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.
3-22
COPYRIGHT©
1992
CANON
INC.
CANON
NP-1550
REV.1
SEPT. 1992
PRINTED
IN
JAPAN (IMPRIMEAUJAPON)
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