01214
is
connected
as
a feedback amplifier with R1214
as
the
feedback element. The
input
resistance
is
made up of
R1211 and the gain-setting
adjustment
R1215. When
not
operating
in
the
X-Y
mode,
the
base of
01214
rises toward
the +15 volt supply
but
is
clamped
at
approximately +5.7
volts by CR1216. This reverse biases
the
base-emitter
junction of
01214.
The base
of
01218
also rises
to
approximately
+5.7 volts. With
the
junction of
R1202-R1219 sitting
at
approximately
O volts,
01218
is
also biased off.
When
the
TIME/DIV switches are set
to
the
X-Y
position (fully counterclockwise),
-8
volts
is
applied
to
the
junction of R1212 and R1217. Also, +5 volts
is
applied
to
the
emitter circuit of
01218
through CR1202. This biases
the Z-Axis Amplifier circuit into
conduction.
At
the
same
time, +5 volts
is
applied
to
the
Channel 1 Scale-Factor
Switching Amplifier circuit (through CR 1201) and
to
pin
18 of the Sweep Control Integrated Circuit U870. This
enables
both
scale-factor indicating circuits
at
the
same
time and disables sweep generation.
Input
Paraphase
Amplifier
01224
and
01234
compose
the
Input Paraphase Ampli-
fier. This
is
an emitter-coupled amplifier stage
that
converts
the single-ended
input
signal
to
a push-pull
output
signal.
The signal
at
the
collector
of
01224
is
opposite
in
phase
to
the
input
signal. The signal
at
the
collector
of
01234
is
in
phase with
the
input
signal. Thermistor resistor RT1230
reduces
in
value with increases
in
ambient
temperature
to
increase
the
gain
of
the
stage. This compensates for changes
in
amplifier gain
that
occur
as
operating temperatures vary.
R1205A and R1205B are
the
Horizontal POSITION and
FINE controls, respectively. The FINE control has approxi-
mately one
tenth
the
range
of
the
POSITION control and
provides fine
adjustment
of a magnified display.
Gain Setting Amplifier
01226
and
01236
are an
emitter
coupled push-pull
amplifier stage.
01244
is
a
constant
current
supply for
the
stage. The gain
of
the
Horizontal Amplifier
is
controlled by
adjusting
the
resistance
connected
between
the
emitters
of
this stage. The
X1
Gain
adjustment
R1237 adjusts unmag-
nified horizontal gain and
the
X10 Gain
adjustment
R1238
adjusts magnified horizontal gain. Magnifier Registration
adjustment R1225 balances quiescent
DC
current
in
01226
and
01236
so
that
a center screen display does
not
change
position when
the
X10 Magnifier
is
turned
on.
@I
Circuit Description-465
When the
BEAM
FIND
pushbutton
is
pressed, R1249
is
connected
to
ground. This reduces
the
current
supplied
through
01244,
which has
the
effect
of
shifting the
operating level
at
the
collector of
01244
in
the
positive
direction. This causes
the
Horizontal Amplifier
to
operate
closer
to
the
point
where signal limiting occurs, thereby
ensuring
that
an overscanned display will remain within the
viewing area
of
the CRT.
Output Amplifier
The push-pull signal from
the
Gain Setting Amplifier
is
connected
to
the
Output
Amplifier through
CR
1253 and
CR
1273. Each half
of
the
Output
Amplifier can be
considered
as
a single-ended feedback amplifier, which
amplifies
the
signal
current
at
the
input
to
produce a
voltage
output
to
drive
the
horizontal deflection plates of
the
CRT. The amplifiers have a low
input
impedance and
require very little voltage change
at
the
input
to
produce
the
desired
output
change. The
Output
Amplifiers are
limited from overdrive by
CR1251,
CR1252,
CR1253, and
CR1273. The
input
diodes
CR1253
and CR1273 become
back-biased when the signal level
at
either
input
becomes
too
positive, and
the
diodes
connected
back
to
back
between the
two
signal
paths
ensure
that
the
signal
amplitude side
to
side
will
be limited
to
a maximum of
about
0.7 volt.
Transistors
01254
and
01274
are inverting amplifier
stages whose collector signals drive
the
emitters of com-
plementary amplifiers
01262-01266
and
01282-01288
respectively. C1256, C1262, and
C1282
provide a signal
path for fast
AC
signal currents from one side
of
the
amplifier
to
the
other.
R1260-R1261 and R1280-R1281
are the feedback elements
in
the
amplifier with C1261 and
C1281 providing high-frequency compensation. The
output
signal from
01262-01266
drives
the
right CRT deflection
plate, while
the
signal from
01282-01288
drives
the
left.
CRT CIRCUIT
General
The CRT Circuit provides
the
voltage levels and control
circuits necessary for
operation
of
the
cathode-ray tube
(CRT). Fig. 3-8 shows a detailed block diagram
of
the CRT
Circuit. A schematic of this circuit
is
shown on diagram 10
at
the
rear
of
this manual.
3-15
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