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7.1
DESCRIPTION
The
Scope
Amplifier board contains the horizontal
and vertical
deflection amplifiers, the horizontal time-
base
generator,
control
circuitry for focus and inten-
sity,
and miscellaneous CRT bias adjustments.
The
Scope Amplifier
operates
in
an auto or
normal
mode. When a triggerable vertical
signal
is
present, a
sweep
is
developed in both auto and normal modes.
When
a
triggerable signal is not present, the
sweep is
blanked in the normal mode and free-running in the
auto mode.
An
external
horizontal
input is available
at
the front
panel.
A block diagram
of
the Scope Amplifier board is
shown
in Figure
7-1, a schematic
in
Figure
7-2,
and
the
printed
wiring
board assembly and parts
list
in
Figure
7-:t
7.2
THEORY OF OPERATION
7.2.1 DEFLECTION AMPLIFIE
RS
The
vertical
and horizontal deflection amplifiers are
identical.
The
input
signal is
initially amplified and
split
into
two
signals, 180
degrees
out of
phase. Each
of these
signals is
then further amplified to
become
a
CRT
deflection-plate
signal. The
amplifiers provide
200V
peak-to-peak
signal
capability with a frequency
bandwidth
of
1
MHz.
7.2.2
HORIZONTAL TIMEBASE
GENERATOR
7.2.2.
1
General
The horizontal timebase
generator
provides
cali-
brated
sweep rates
over a
six-decade
range
from
1jlsec
to 100 msec per division. Sweep-rate
selection
origi-
nates
from the
processor via
the
signal lines for the
SCOPE
SWEEP CONTROL 0-3.
Vernier
control
over
the sweep
rate is
generated
by
the
sweep-vernier
volt-
age
input
from
the front panel.
7.2.2.2
Ramp Generator
The
ramp
signal
is
developed using an integrator
(U:l)
with a constant
voltage.
The
sweep
rate
is
deter-
mined
by R5,
R6, R7
and
C3,
C4,
and
C5.
The
combi-
nation
of
the
RC
network
produces
the six
sweep
rates.
7.2.2.3
Blanking and Trigger
Hold-Off
Circuitry
When
the
ramp
voltage reaches
+2.7V,
the output
7-1
SECTION 7.
SCOPE AMPLIFIER BOARD (A2)
of UllB
produces a blanking pulse
which is used to
short-circuit the
ramp
integrator
and
trigger the hold-
off· integrator
(U5).
The hold-off rate
is
determined by
R19,
C14, and
C15.
The
combination of
the RC
net-
work
produces two hold-off times, one for msec
and
one
for 11sec. When
the hold-off
ramp reaches +2.7V, the
output
of
U11A
short-circuits the hold-off'
integrator,
and the
sweep
generator
awaits a
sweep trigger.
Sweep
trigger
is
either
in
auto or normal
mode
as
selected
by
the AUTO/NORMAL
trigger-select via
the
front
panel. In
the
normal mode,
UllB
is
always dis-
abled,
thus keeping
the
blanking
signal
high and
pre-
venting
the
ram
p
from starting until
a
trigger
pulse
is
present. In
the
auto
mode,
if
the SYNC
PRESENT
input
is
high,
indicating
no sync,
the scope
sweep
i5
5elf-triggered. If there
is a
sync, the
sweep will
wait fo
r
a
pulse
on the
TRIG PULSE
line
to
start
the 5weep.
NOTE
The
entry
of a scope
trigger
delay
will prevent
operation of
scope
triggering
as long
as
the
unit is
set
on ,;MODULATION,
Tone
Seq."
7.2.3
HORIZONTAL SWITCHING
The
input
to the
horizontal
deflection amplifier
is
selected
between
two
sources.
The first
source
is
the
INT HORIZ IN
signal li ne,
which provides
the
hori-
zontal character
sweep
and t he
horizontal
spectrum
-
analyzer sweep.
The other
source
is
the scope-mode
signal path
from
t
he horizontal
positioning-summing
amplifier.
The
scope-mode
signal
is
the
output of
either
the horizontal time base
generator or the
EXT HORIZ
INPUT
from the
front
panel. The
SCOPE
MODE
EN
line
from the
processor
selects either internal
horizon-
tal or scope-mode
horizontal
inputs.
The EXT HORIZ
EN
line
selects
one
of
the
two
scope-mode signals.
7.2.4
Z-AXIS MODULATOR
A
crossover
network provides
CRT
Z-AXIS
modu-
lation from de
to 1
MHz.
A
high-pass
and
low-pass
network
on t he High-Voltage
P
ower
Supply
board
(Al)
produces
a crossover
frequency of
16Hz.
The Z-AXIS
modulator circuit
is
the high-frequency
modulation
path,
16 Hz
to
1
MHz.
The
resulting CRT
Z-AXIS signal
is
capacitively
coupled on
the
High-Voltage Power
Supply
board
(Al)
to
the CRT grid. The
low-frequency path,
de to
16
Hz,
is
through the
intensity-control
circuit.
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