Service manual
IMl015
driver
at
the
high
frequencies
to
compensate
for
the
capacitance
in
QllO and
at
the
cathode
of
the
CRT.
The
signal
at
the
collector
of
QllO
is
direct
coupled
to
the
base
of
the
emitter
follower
Qlll,
which
provides
a low
source
impedance
for
driving
the
cathode
of
the
CRT.
Vertical
retrace
blanking
is
applied
to
the
base
of
Ql09,
which
conducts
harder
during
this
time
to
increase
the
voltage
at
Qlll
emitter
and
drives
the
cathode
of
the
CRT
to
cutoff.
R227
and
C159
forms a
protection
circuit
for
the
output
stages
in
the
event
of
a
CRT
arc.
If
a
transient
voltage
of
230
volts
or
greater
appears
at
the
CRT
cathode,
ionization
will
take
place
within
the
arc
gap,
providing
a low
impedance
path
to
ground.
3.3
SYNC
PROCESSING
The
sync
processing
circuit
consist
of
Ql12, Ql14,
Ql15 and
QllS.
The
func-
tion
of
this
circuit
is
to
provide
negative
vertical
sync
pulses
to
drive
the
vertical
oscillator
and
positive
horizontal
pulses
for
the
AFC
circuitry.
A
positive
going
composite
video
signal
at
the
collector
of
Ql03
is
applied
directly
to
the
base
of
the
sync
amplifier
Ql12.
This
amplifier
has
a
vol-
tage
gain
of
S and
it
applies
an
amplified
composite
video
signal
to
the
base
of
Ql14,
the
sync
stripper.
CllS
is
used
to
remove
the
3.5SmHz
color
burst
signal
from
the
back
porch
of
the
horizontal
pulse.
Ql14
is
turned
on when
triggered
by
the
leading
edge
of
the
sync
pulse
and
is
turned
off
by
the
trailing
edge
of
the
sync
pulse.
This
on/off
action
of
Ql14
results
in
a
negative
going
composite
sync
signal
of
approximately
l3.5V
p-p
at
its
col-
lector.
The
composite
sync
signal
is
sent
through
a
vertical
integrator
(R14S
and C122)
to
the
base
of
Ql15,
the
vertical
sync
separator.
The
vertical
sync
signal
at
the
collector
of
Ql15
is
used
to
trigger
the
vertical
oscillator
Ql16. The
zener
diode
in
the
collector
circuit
of
Ql15
is
used
to
limit
the
peak
to
peak
amplitude
of
the
vertical
sync
pulse
to
6.2V.
The
vertical
portion
of
the
composite
sync
signal
is
removed by
the
differen-
tiator
circuit
C129
and R167. The
horizontal
pulse
is
applied
to
QllS,
in-
verted
and
used
to
drive
the
AFC
stage
Ql19.
3.4
VERTICAL DEFLECTION
The
vertical
deflection
circuit
consist
of
a
vertical
oscillator,
an
emitter
follower,
a
vertical
output
amplifier
and
the
vertical
deflection
coil
of
the
yoke.
The
vertical
oscillator
Ql16
is
synchronized
by
the
vertical
sync
pulse
from
Ql15 and
it
produces
a
sawtooth
waveform
signal.
This
signal
is
fed
through
an
emitter
follower
to
the
input
of
the
vertical
output
amplifier
Ql.
This
amplifier
provides
a
sawtooth
current
waveform
for
the
vertical
deflection
coil
of
the
yoke.
3-2