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Circuit Description—Type
3B4
Q105
immediately
removes
the current through
R115 from
D143.
This biases D143 to 3.8 ma and the circuit operates as
if the TRIGGER
MODE
switch were in the NORM
position.
The Auto Multi remains in its unstable state for approximate-
ly 80 milliseconds or less.
If a second trigger pulse is re-
ceived during the time the Auto Multi is in its unstable mode,
it switches sweep gating diodes D143 via D141 and initiates
a sweep.
This second
trigger pulse also signals the Auto
Multi to stay in its unstable state for an additional 80 milli-
seconds,
As long as incoming trigger pulses arrive at inter-
vals shorter than about 80 milliseconds, the sweep
is trig-
gered and operates as if the TRIGGER
MODE
switch were
set
to
NORM.
If the
interval
between
incoming
trigger
pulses
is longer
than
80 milliseconds,
the Auto
Multi
has
time to return to its stable state, and the Sweep Generator
resumes free-run operation.
For this reason, the AUTO mode
should not be used where the interval between trigger pulses
exceeds 80 milliseconds.
Since the arrival of just one trigger pulse does not start
a sweep, but merely removes the circuit from a free running
condition, it is probable that the trigger pulse which switches
the Auto Trigger Multi will arrive while a free-run intiated
sweep is in progress.
In this case the Sweep Generator can-
not become triggerable until the end of the holdoff period
for the sweep in progress, but from then on, every sweep will
be a triggered sweep
if the reptition rate of the incoming
trigger pulse
is greater than
about 20 pulses per second.
Whenever
the
period
between
trigger
pulses
exceeds
80
milliseconds, the Auto Trigger Multi reverts to its stable state
and C105 charges up.
With C105 charged, enough current
is again
available
through
R115
to switch
D143
and
free
run
the
Sweep
Generator.
The
Auto
Trigger
Mutli
incidentally
controls
the circuit
which
lights the single sweep
READY
and
SWEEP
TRIG'D
lamps.
In both the AUTO
and
NORM
modes,
the switching
of the Auto Trigger Multi cuts off Q114.
As the collector of
Q114 rises toward the +125 volt source, the voltage increase
lights the SWEEP
TRIG'D
lamp (B119).
SINGLE
SWEEP
Mode.
As previously explained
in the
NORM
Mode
discussion, the Lockout Multi switches when the
holdoff capacitor discharges after the retrace portion of the
sweep.
After the holdoff capacitor discharges down to where
D179
becomes
forward
biased,
the
current
through
R175,
R177,
R124,
R126
and
R127
applies
cutoff
bias
to
Q135.
However,
in the SINGLE
SWEEP
mode
of operation,
R177
ig connected
to
+125
volts,
which
serves
to
keep
D179
reverse biased at all times.
As the TRIGGER MODE
switch
is turned from
NORM
position to the SINGLE SWEEP posi-
tion, switching
transients trigger the sweep.
As the sweep
runs
up, D178
becomes
forward
biased
and
makes
Q135
the
conducting
transistor
of the
Lockout
Multi.
Since
the
+125
volts
connected
to
R177
keeps
D179
reverse
biased,
the
Lockout
Multi
stays
locked
up with
Q135
conducting.
The
conduction
of Q135
diverts all current from
D143
so
that
it cannot
switch
and
start
a
sweep.
To
unlock
the
Lockout Multi, if is necessary to press the PUSH
TO
RESET
switch
(SW135].
Pressing
the
PUSH
TO
RESET
switch
ap-
plies —100
volts through
R137 to C136.
When
the voltage
across C136 becomes great enough to fire neon bulb B135,
the
current
through
B135
and
R135
generates
a
negative
pulse which
is coupled
through
C135
to the Base of Q135.
The negative pulse cuts off Q135 and switches the Lockout
Multi,
With
Q135
cut off, the current
through
R144
and
R145 arms D143 so that it will switch to its high state when-
ever a trigger pulse is applied.
The current through Q125
forward
biases Q114
and
turns on the READY
lamp.
The
Sweep
Generator
will now
deliver a single sweep
upon
the
application of a trigger pulse.
Horizontal
Amplifier
The block diagram
in Section 5 shows the basic arrange-
ment of the horizontal
amplifier circuits.
The input to the
Horizonte!
Amplifier
proper
is taken
from
the
output
of
cathode follower V173A in the Miller Runup circuit. Normal-
ly, the signal input to the Horizontal Amplifier is the sweep
ramp
voltage.
However,
when
the
TIME/DIV
OR
HORI-
ZONTAL
VOLTS/DIV
switch
is set to the EXT
HORIZ
IN
position, the signal on the grid of V173A is taken from the
External Horizontal Amplifier consisting of V161B and Q234.
As shown
on the Sweep
Generator
schematic,
the high
impedance
EXT HORIZ
IN input is applied to cathode fol-
lower
V161B
which
in turn
drives common
base amplifier
Q234.
Coupling
between
the input cathode
follower and
the common
base
stage
is by
means
of a
resistor string
which
includes
the EXT
HORIZ
GAIN
and
VARIABLE
con-
trols.
The
EXT
HORIZ
GAIN
contro!
is a screwdriver ad-
justable control that is set during calibration.
The VARIABLE
control
is an uncalibrated
front panel
control that permits
the operator
to decrease the sensitivity of any of the five
SEC OR
EXT VOLTS
steps over a range from 1:1 to = 2.5:1.
Referring to the Horizontal Amplifier schematic in Section
5, the input from the Miller Runup cathode follower is applied
through
R401, R402, and
D411
to the base of input transistor
Q414.
SWP CAL contro! R402 provides a means of adjusting
the amount of signal drive to the Horizontal Amplifier.
Front
panel
FINE
and
POSITION
controls
apply
de voltages
to
the base of Q414, which
in turn establishes the operating
points of the transistors
in the output stages
of the Hori-
zontal Amplifier.
(Changing the de level around which the
transistors operate changes the position of the sweep on the
crt screen.)
Diodes D413, D414, and D415 protect Q414 from
excessively
large
signals
when
externally
generated
hori-
zontal
input signals are used.
The output of Q414 is applied to the input of a paraphase
amplifier
consisting
of Q424,
Q434,
Q423,
Q433,
and
as-
sociated circuit elements.
The two transistors in each side of
the paraphase amplifier are compound connected to achieve
the
high
effective
gain
needed
to
make
the
stage
gain
dependent only upon the coupling resistors between the two
sides of the paraphase.
The coupling network between the
two
sides
of the
paraphase
include
the
SWP
MAG
REGIS
resistor
R422,
the
X50
MAG
GAIN
resistor R447,
and
the
MAG
resistors
R340A
to
R340R.
The
coupling
resistance
value
is about 9202
when
no magnification
is used (X1}
and is decreased to about 202 for X50 magnification (see
Magnifier Switch Schematic].
The output of the paraphase amplifier drives the cathodes
of a grounded-grid, push-pull connected twin triode (V444A
and V444B).
The push-pull output of the twin triode is ap-
plied through pins 17 and 21 of the interconnecting plug to
the horizontal deflection plates of the crt.
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