Circuit
Description-465
of the transistors begins
to
conduct;
for example,
0374.
The negative level
at
the
collector of
0374
forward-biases
CR305
and CR307 and back-biases CR304 and
CR308
preventing
the
Channel 1 signal from reaching
the
Delay-
Line Driver stage. Meanwhile,
the
Channel 2 Diode Gate
passes
the
Channel 2 signal
to
the
Delay-Line Driver stage.
The frequency-determining
components
in
the CHOP
mode are C368, R368, R370, and R378. The switching
action occurs
as
follows: when
0374
is
on,
C368
attempts
to
charge
to
-8
volts through R368. The
emitter
of
0364
slowly goes toward
-8
volts as C368 charges. The base
of
0364
is
held
at
a
point
determined by
the
voltage divider
R365 and R374 between
-8
volts and
the
collector level of
0374.
When
the
emitter
voltage
of
0364
reaches a level
slightly more negative
than
its base,
0364
conducts. Its
collector level goes negative and pulls
the
base
of
0374
negative through divider R364-R375
to
cut
0374
off. This
switches
the
Diode Gate stages
to
connect
the
opposite
channel
to
the
Delay-Line Driver stage. Again, C368 begins
to
charge towards
-8
volts
but
this
time
through R378.
The
emitter
of
0374
slowly goes negative
as
C368 charges
until
0374
turns
on.
0364
is
shut
off
and
the
cycle begins
again.
The Chop Blanking Amplifier stage,
0358,
provides an
output
pulse
to
the Z Axis Amplifier circuit which blanks
out
the
transition between
the
Channel 1 and
the
Channel 2
traces. When
the
Switching Multivibrator stage changes
states,
the
voltage across
T354
momentarily increases. A
negative pulse
is
applied
to
the
base of
0358
to
turn
it off.
The width
of
the
pulse
at
the
base of
0358
is
determined
by R356 and C356.
0358
is
quickly driven
in
to
cutoff
and
the positive going
output
pulse, which
is
coincident with
trace switching,
is
connected
to
the
Z Axis Amplifier circuit
through R359.
Added
Mode Operation. When
the
ADD
pushbutton
is
pressed,
the
fol lowing occurs:
1.
+5
volts
is
applied
to
the
cathodes
of
CR305 and
CR307 through R371.
2. +5 volts
is
applied
to
the
cathodes
of CR315 and
CR317 through R361.
3.
-8
volts
is
applied
to
the
junction of R321 and
R322.
The first
two
actions enable
both
of
the
Channel Diode
Gates so
that
the
signal applied
to
the
Delay Line Driver
stage
is
the
algebraic sum
of
the
Channel 1 and Channel 2
signals. The
-8
volts applied
to
R321
and
R322 provides
sufficient
current
to
keep
both
diode gates
turned
on
without
altering the
DC
levels associated with
the
Delay
Line Driver stage.
Delay-Line Driver
The
outputs
from
the
Diode Gate stages are applied
to
the
Delay-Line Driver stage composed of
0322
and
0324.
3-8
0322
and
0324
are
connected
as
feedback amplifiers with
R325 and R327 providing feedback from
the
collector
to
•
the
base of their respective transistors. A sample of
the
•
signal
in
the collector circuit
of
0322
is
used for triggering
in
the NORM mode of trigger
operation.
The
BW
LIMIT
switch S338A connects a pi filter
composed
of C338, C339,
L338, and L339 between
the
output
signal lines of
the
Delay-Line Driver stage
to
reduce
the
upper
-3
dB
band-
width limit
of
the
Vertical Amplifier system
to
approxi-
mately 20 MHz. R335 and R336 provide reverse termina-
tion for
the
delay line. The TRIG VIEW switch S338B
connects the
output
of
the
Trigger View Amplifier
to
the
input
of
the Delay Line
in
place
of
the
Delay Driver Stage.
This allows viewing
the
trigger signal present
in
the A
Trigger Generator Circuit.
Reference Feedback Amplifier
Reference Feedback stage
0332
provides
common
mode
voltage feedback from
the
Delay-Line Driver stage
to
allow
the
diode gates
to
be
switched with a minimum amplitude
switching signal. The
emitter
level
of
0332
is
connected
to
the
junction of the Switching Multivibrator collector
resistors, R371 and R361
through
CR372
or CR362. The
collector level of
the
"on"
Switching Multivibrator tran-
sistor
is
negative and
either
CR362
or
CR372
is
forward
biased. This clamps the
cathode
level
of
the
forward biased
shunt
diodes
in
the applicable Diode Gate
about
0.5 volt
more negative than
the
emitter
level
of
0332.
The
level
at
the
emitter of
0332
follows
the
average voltage level
at
the
II/#
emitters of the Delay-Line Driver stage. The
shunt
diodes •
are clamped near their switching level and therefore, can be
switched very fast with a minimum amplitude switching
signal. This maintains
about
the
same
current
through the
Diode Gate
shunt
diodes so
they
can
be
switched with a
minimum amplitude switching signal regardless of
the
deflection signal
at
the anodes
of
the
shunt
diodes.
Normal Trigger Pickoff Amplifier
The trigger signal for NORM trigger operation
is
obtained from
the
collector
of
0322.
Normal Trigger
DC
Adjustment R340 sets
the
DC
level
of
the
normal trigger
output
signal so
the
sweep
is
triggered
at
the
O
level
of the
displayed signal when
the
Triggering LEVEL control
is
set
to
0.
0344
and
0346
are
connected
as a feedback amplifier
with the signal applied
to
the
non-inverting input and the
feedback
connected
between
the
output
and
the
inverting
input. Gain
of
the
stage
is
approximately:
R348 + R344
R344
VERTICAL
OUTPUT
AMPLIFIER
General
The Vertical
Output
Amplifier circuit provides the final
amplification for the vertical deflection signal. This circuit
()'
includes
the
Delay Line
and
the
BEAM FIND
pushbutton.
'--
The BEAM FIND
pushbutton
compresses an overscan
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