Service manual
IM1015
C158
serves
to
block
DC
currents
through
the
yoke and
to
provide
usn
shaping
of
the
current
waveform. "S"
shaping
compensates
for
stretcnlng
at
the
left
and
right
sides
of
the
picture
tube
because
the
curvature
of
the
CRT
face
and
the
deflected
beam
do
not
describe
the
same
arc.
L103
is
an
adjustable
width
control
placed
in
series
with
the
horizontal
deflec-
tion
coils.
The
variable
inductive
reactance
allows
a
greater
or
lesser
amount
of
the
deflection
current
to
flow
through
the
horizontal
yoke and
varies
the
width
of
the
horizontal
scan.
The
positive
flyback
pulse
developed
during
horizontal
retrace
time
is
recti-
fied
by CRl16 and
filtered
by C148.
This
produces
approximately
600
VDC
which
is
coupled
through
the
focus
control
R219
to
G4
of
the
CRT.
The
resistive
divider
R221
and
R225
provides
approximately
400
VDC
for
the
G2
of
the
CRT.
This
same
pulse
is
transformer
coupled
to
the
secondary
windings
of
T3.
It
is
rectified
by
CRl
and
R5
to
provide
18kV
for
the
CRT
anode.
It
is
also
rectified
by
CR120
to
provide
a -80 V
source
for
the
brightness
control
R4.
In
the
event
the
-55 V
supply
voltage
rises
excessively
due
to
a
failure
in
the
regulator
circuit,
Q128
will
conduct
and
shunt
the
+18Vsupply
for
Ql18
through
Q122
to
ground.
This
will
shut
dO~T!
the
high
voltage
supply
of
the
monitor
and
prevent
X
radiation.
R212
is
a
selected
resistor
(for
replacement
of
R212,
see
section
4.2)
that
enables
Q128
to
conduct
when
the
+55
volt
supply
exceeds
59 V ±lV.
3.6
AUTOMATIC
FREQUENCY
CONTROL
The
function
of
this
circuit
is
to
compare
the
phase
(frequency)
of
the
hori-
zontal
oscillator
with
the
incoming sync
signal
and
generate
a
DC
control
vol-
tage
which
holds
the
oscillator
in
phase
lock
with
the
input
sync
signal.
The
automatic
frequency
control
circuit
consists
of
stages
Ql18, Ql19 and Q123.
The
composite
sync
coupled
from Ql14
is
differentiated
at
Ql18 and
fed
to
phase
splitter
Ql19. The
positive
and
negative
balanced
sync
outputs
of
Ql19
and
applied
to
the
diode
phase
detector
CRill
and CRl12. Also
applied
to
the
diodes
is
a
sawtooth
voltage
derived
from
the
horizontal
flyback
pulse
by
the
way
of
Q123
and
integrator
R173
and C134. The
phase
compared
output
appears
as
a
DC
correction
voltage
after
filtering
by R179,
C135
and C136.
This
correction
voltage
is
then
applied
to
the
base
of
Q121
to
effect
frequency
control.
3.7
LOW
VOLTAGE
POWER
SUPPLY
The low
voltage
supply
module
is
capable
of
operating
from
AC
line
voltage
of
100V, 120V,
220V
or
140V, SOi60Hz.
The power
supply
input
voltage
is
determined
by
the
setting
of
the
two
slide
switches
located
at
the
rear
of
the
supply.
These
switches
are
stamped
to
indicate
the
appropriate
line
voltage
setting.
3-5