circuit.
Triggering becomes a funtion of the trigger signal
When the emitter voltage of Q752 steps up, Q771 is turned
amplitude and the slope of the trigger signal.
on hard. This applies forward bias to the disconnect diode,
and timing current plus extra base current is now supplied
The Trig Level Centering R724 is adjusted with the Trigger
by Q771. The Miller circuit now starts to run down and will
LEVEL control set to zero volts. It is adjusted so a low ampli-
continue to run down until diode D770 is forward biased.
tude input signal will trigger the trigger generator with the
This occurs when the emitter potential is approximately 0.6
SLOPE switch in either the + or - position.
volts more negative than the 1.3 volt potential on the base of
Q770. This turns Q770 on. It now shares part of the available
The trigger generator consists of the comparator Q730-
current. The rundown of the Miller circuit levels off and a
Q731, the tunnel diode D737 and the amplifier Q740. In
condition of equilibrium is maintained. The output voltage
the quiescent state, with the trigger generator ready to be
level of the Miller circuit remains near O V until the next gate
triggered, the comparator is unbalanced so Q730 is conduct-
is applied to the gate comparator, when it again runs up to
ing most of the current. The current of Q731 sets the tunnel
generate another sweep ramp.
diode between its low operating and threshold state.
Diode D782 conducts if the positive voltage excursion
If the current through Q731 is increased by the application
on the base of Q790 should be excessive. This prevents the
of a trigger signal (negative-going signal on the base of
Miller circuit from hanging up.
C2730 or positive-going signal on the base of Q731) the tunnel
diode will shift to its high state. When the TD shifts to its
Holdoff Circuit. When the sweep gate is applied to the
high state, a fast-rise pulse is generated at the base of the
emitters of the gated comparator, the collector of Q770 steps
amplifier Q740, This generated trigger pulse is amplified,
down from approximately 0 volts to -1.4 volts (drop across
inverted and applied us a positive-going pulse to the sweep
D767 and D768). The negative-going gate to the base of
gating multivibrator Q750-Q751. The output waveform of
Q761 is amplified and applied to Q760 as a positive-going
the multi vibrator is the sweep gate to the sweep circuits
gate. This turns Q706 on hard. The resultant current demand
and the CRT unblanking signal.
of Q760 through R741 pulls the emitter of the trigger amplifier
Q740 down far enough to cut Q740 off. No trigger signal
Sweep Gating Multivibrator. The positive-going input
can now get through from the trigger generator to the sweep
pulse from the collector of Q740 turns Q750 on and flips
gating multivibrator.
the multivibrator. This applies a negative-going gate to
the emitter follower Q752 which provides the unblinking
When the sweep gating multivibrator is flipped to its
pulse for the CRT blanking plates and the sweep gate signal
pretriggered state by the sweep ramp on the base of Q751,
to the emitters of the gated comparator Q770-Q771. The
the positive-going gate at the emitter of Q752 is not suf-
sweep gating multivibrator is a bistable oscillator so it
ficient to turn Q770 on. The sweep ramp must run down
will remain in this state until a signal is applied to the circuit
to approximately 0.6 volts to turn D770 on. After a time
to switch the multivibrator back to its pretriggered state.
delay period, established by the RC feedback network (C761
and R762 between the collector and base of Q760), the
The sweep gate signal steps the emitter potential of
collector current of Q760 will decrease. This increases the
the gated compartor Q770-Q771 from approximately 1 volt
forward bias of Q740 to the point where it again conducts
to 0 volt. The DC level on the base of Q771 is approximately
and an applied trigger signal to the amplifier will now go
300 mV (set by the voltage divider R779 and R778). The base
through the amplifier to trigger the sweep gate multivibrator
voltage of Q770 is approximately 1.3 volts (set by the 10:1
and initiate another sweep.
voltage divider R770 and R771). Both sides of the comparator
are therefore back biased when the negative-going gate is
Sweep rate is a function of the timing resistors R785 and
applied to the emitters. The collector of Q771 steps down
timing capacitors C785. R786 is the VARIABLE control which
abruptly, gate diode D781 disconnects and the Miller runup
provides an approximate 2.5 times sweep rate change be-
circuit action is initiated.
tween the TIME/DIV selector (SW785) positions.
S w e e p G e n e r a t o r . When diode D781 disconnects, col-
Horizontal Amplifier. The sawtooth voltage at the emitter
lector current from Q771 is interrupted so the base of Q790
of Q800 drives the paraphase amplifier Q810-Q820 which
starts toward the -10 volt supply.
converts the single-ended sweep from the sweep generator
to a push-pull drive signal for the horizontal deflection plates.
The Miller runup circuit is essentially a high gain amplifier
The paraphase output amplifier is long-tailed to the constant
employing negative feedback, The positive-going voltage at
current source Q830 and Q831. Horizontal gain is provided
the collector of Q791 is fed back through runup emitter fol-
by the GAIN adjustment R813. Horizontal trace positioning is
lower Q800 and coupled through the timing capacitor C785
provided by the POSITION control R823 which shifts the DC
to the base of Q790. This feedback voltage opposes the
output level to the horizontal deflection plates.
tendency for the base to swing negative. Because the gain of
the amplifier Q790-Q791 is high, a very linear rate of charge
is maintained on the timing capacitor C785. Timing current
through R785 almost equals the charging current of C785 so
CRT and Blanking Circuit
the base of Q790 moves only a very small amount during run-
This circuit contains the high voltage generating and
up.
regulating circuits for the accelerating potentials on the
The linear voltage rise at the emitter of Q800 rises to
CRT, plus an unblinking circuit, and a baseline suppressed or
approximately 7.5 volts (set by the Sweep Length adjust-
intensifier circuit.
ment R759) and pulls up the base of Q751 to its forward bias
High Voltage Circuit. The high voltage oscillator Q1003
state. At this point the gating multivibrator is flipped to its
drives the primary windings of the high voltage transformer
pretriggered state. The emitter of Q752 now steps up to
T1010. The high voltage rectifier circuit, containing D1014
approximately
+9
volts.
3-13
