Q2
P2S
Pl-~~
.047
STEP
AMPL.
Rll
lOOK
STEP
SCAN
-----+--------<--------<-----<.....,.___
+12.0V
RIO
IN
lK
vvv
R9
3.3K
FROM
c
4
SYNCH
SHAPER
IC1
0.1
01
C6
7638
~
VERT
RB
DSC
3.3K
Rl2
250K
HEIGHT
5
..
3.5V
VERT.
LIN.
+
Cll
1·7
Q3
7639
VERT
ORI
VER
TO
VERT.
---OUTPUT,
Q4
Figure
10.
Vertical Oscillator/Driver and StepScan Amplifier Circuits
VERTICAL
OSCILLATOR
(Refer
to
Figure 10.)
The
negative-going vertical sync pulses are AC
coupled
(C4)
to
the
gate
of
a programmable
unijunction
transistor de-
vice,
01.
This device
turns
on
with
each negative-going
sync pulse applied
to
its gate. This action permits C6
and
Cl
to
discharge very rapidly;
then
recharge slowly during
the
period
that
a sync pulse
is
not
applied
to
the
gate. The
recharge
path
for
C6 and
Cl
is
through
R 12 and R 13.
As
soon
as
the
next
sync pulse
is
applied
to
the
gate
of
01,
C6
and
Cl
discharge very rapidly again. This sequence
of
events produces a positive-going
ramp
or
sawtooth
wave-
form
at
the
anode
of
01.
When no vertical sync pulses are
connected
to
the
monitor,
vertical oscillator 01
is
kept
free-running
to
maintain a
raster on
the
CRT. This
is
accomplished by biasing
the
gate
of
01 in
conjunction
with
the
charge and discharge
action
of
C6 and
Cl.
Resistors R9
and
R8 provide
the
proper
bias
for
01,
which also
determines
the
repetition
rate
for
the
charge and discharge
action
of
C6
and
Cl.
In
addition, during no-signal
conditions,
components
05
and
02
(in
conjunction
with
01).
provide a small incre-
mental voltage above
ground
to
compensate
for
the
base-
emitter
voltage
drop
of
the
vertical driver,
03.
This
is
necessary
to
keep
the
vertical
output
stage,
04,
from being
driven into
cutoff,
which could result
in
distorted
vertical
linearity.
VERTICAL
DRIVER
(Refer
to
Figure 10.)
The positive-going
sawtooth
waveform, from
the
anode
of
4-25
01,
is
direct
coupled
to
the
base
of
vertical driver
03,
which
operates
as
an
emitter
follower. The
sharp
fall
time
of
the
sawtooth
is
a result
of
the
rapid discharge
of
C6 and
Cl
through
01.
The
amplitude
of
the
sawtooth
is
varied
with
the
HEIGHT
control,
R12.
A~
' '
I I
I '
B~
I '
'
'
I o
c~
'
PARABOLA
AT
JUNCTION
OF
C6AND
C7
VERTICAL
DRIVE
WITHOUT
VERT
PARABOLA
ADDED
PARABOLA
PULSE
AND
VERTI-
CAL
SAWTOOTH
ADDED
TOGETHER
TO
PRODUCE
THE
REQUIRED
VERT
DRIVING
SIG-
NAL.
::·
__
.
./1
__
.-·
--·
/1_/,
~~~~~~~~
~~~~Es~~;~~~~AL
0
V('
l/.-
I
ADDED
-
NOTE
INCREASED
:A,::::,:
~
-----
AMPLITUDE!
SAWTOOTH
WITHOUT
STEPSCAN
The
output
sawtooth
from
the
emitter
of
03
is
direct
coupled
to
the
base
of
vertical
output
stage,
04.
Part
of
this
sawtooth
waveform, however,
is
also
coupled
back
to
the
junction
of
C6
and
Cl
via R18 and VERT. LIN.
control
R 11 for
proper
shaping. Since this path
is
resistive,
the
waveform will be integrated
into
a parabola waveform
by
C7
(waveform A). This results in a
predistortion
of
the
drive
sawtooth
(waveform C). (Waveform B illustrates
the
drive
sawtooth
without
parabola shaping.) Parabola shap-
ing
is
necessary
to
compensate
for
the
non-linear charging
of
C6 and
Cl.
An additional
path
for
phase
compensation
is
provided
through
C12
and
R 19.
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