During no-signal conditions,
0100
is
off. Transistor
0101,
however,
is
forward biased by
the
6.2
volts
on
its base,
which
is
established by zener diode D100. When a video
signal
is
applied
to
the
base
of
0100,
it
conducts,
which
caus.es forward biased
0101
to
conduct.
The
resultant
out-
put
is
developed across R
104
at
the
collector
of
0101;
then
DC
coupled
to
the
cathode
of
V1
(CRT) via peaking coil
L 100 and R113. Resistor R113 isolates
0101
from tran-
sients
that
may
occur
as
a result
of
CRT
arcing. Capacitor
C101
shunts
to
ground high frequency video
that
may
appear
on
the
base
of
0101.
Peaking coil L
100
boosts
the
high frequencies of
the
video signal. Capacitor C103 pro-
vides additional filtering
of
the
+ 70V, while C102
is
a high
frequency
AC
bypass capacitor.
HORIZONTAL SYNC AMPLIFIER
(Refer
to
Figure 4.)
The horizontal sync amplifier consists
of
one stage,
050,
which operates
as
a switch. During a no-signal
condition,
050
is
off. When a positive-going horizontal sync signal,
approximately
4.0
volts P-P,
is
applied (DC coupled)
to
the
base
of
050,
it goes into saturation.
The
amplified
output
is
developed across load resistor R51,
approximately
35V,
which forms a voltage divider with R77. The negative-
going horizontal
sync
pulses are
AC
coupled
to
the
phase
detector
circuit via
the
R-C
network
consisting
of
R52 and
C68, a high frequency pass filter.
PHASE DETECTOR
(Refer
to
Figure 5.)
The phase
detector
consists
of
two
diodes ( D50 and D51)
in
a keyed clamp circuit. Two inputs are required
to
gener-
ate
the
required
output,
one
from
the
horizontal sync
amplifier,
050,
and
one
from
the
horizontal
output
circuit,
054.
The required
output
must be
of
the
proper polarity
and
amplitude
to
correct
phase differences between
the
input horizontal sync pulses and
the
.horizontal time base.
The horizontal
output
(054)
collector pulse
is
integrated
into a
sawtooth
by R56 and C69. During horizontal sync
FROM
HORIZ.
SYNC
AMPL.,050
R53 R54
C69
.0021
C52 +
1.1
R58
4.7k
R56
150K
1/2W
FROM
+70V
+---SOURCE
VIA
T
.00
5
C72 R76,
3.3K
C51
14.7
~-----•
FROM
HORIZ.
OUTPUT,
054
050
A6J
HORIZ
SYNC AMP
Pl-6
HOR-;t:--hNW----4_.
SYNC
C68
R52
PPF2.2K
TO
PHASE
DETECTOR
+70V
Figure
4.
Horizontal Sync
Amplifier
Circuit
time, diodes D50 and
D51
conduct,
which
shorts
C69
to
ground. This effectively clamps
the
sawtooth
on
C69
to
ground
at
sync time.
If
the
horizontal time base
is
in
phase
with
the
sync (waveform A),
the
sync pulse will
occur
when
the
sawtooth
is
passing
through
its
AC
axis and
the
net
charge on C69 will be zero (waveform
B).
If
the
horizontal
time base
is
lagging
the
sync,
the
sawtooth
on
C69 will be
clamped
to
ground
at
a
point
negative from
the
AC axis.
This will result
in
a positive
DC
charge
on
C69 (waveform
C). This
is
the
correct
polarity
to
cause
the
horizontal
oscillator
to
speed
up
to
correct
the
phase lag. Likewise, if
the
horizontal
time
base
is
leading
the
sync,
the
sawtooth
on C69 will be clamped
at
a point positive
from
its AC
axis. This results
in
a
net
negative charge
on
C69, which
is
the
required polarity
to
slow
the
horizontal oscillator
(waveform D).
Components
R55, C52, R58
and
C53 com-
prise
the
phase
detector
filter. The bandpass
of
this filter
is
chosen
to
provide
correction
of
horizontal oscillator phase
without
ringing
or
hunting. Capacitor C50
times
the
phase
detector
for
correct
centering
of
the
picture
on
the
raster.
HORIZONTAL OSCILLATOR
(Refer
to
Figure 5.)
The horizontal oscillator consists
of
051,
which
is
em-
ployed
as
a modified
type
of
Hartley oscillator. The
051
A6J
HORIZ
OSC
TO
HORIZ.
~~£2..-
PULSE
SHAPER,
052
A
B
c
D
0
0
0
REFERENCE
HORIZ.
SYNC
OSC
ON
FREQ
NO
CORRECTION
VOLTAGE
OEVELOPEO
OSC
SLOW,POS
CORRECTION
VOLTAGE.
OSC
FAST,
NEG
COR"RECTION
VOLTAGE
Figure 5. Phase Detector
and
Horizontal Oscillator Circuits
4-22
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