TM 11-6625-2735-14-1
The sawtooth voltage waveform from the Delaying
Sweep Generator is connected to the gate of Q926B. The
quiescent level of the delaying sawtooth biases Q926B on
and its drain is negative enough to bias Q938B on. Q926A
and Q938A are off and not conducting. As the Delaying
Sweep sawtooth voltage goes down, the gate of Q926B
also goes down. When it goes more negative than the level
at the gate of C926A (established by the DELAY TIME
POSITION control), C926A conducts and Q926B turns
off. This also switches the states of Q938A and B and
produces a positive-going rectangular current pulse at the
collector of Q938A. This initiates the B sweep when B
TRIG SOURCE is set to STARTS AFTER DELAY or
enables the B Trigger Tunnel Diodes in all other positions
of B TRIG SOURCE switch. When the Delaying Sweep
resets, Q926B again conducts and Q926A is turned off.
This switches C938A and B back to their original states.
Non-Delaying Sweep Generators
There are two Non-Delaying Sweep Generators. In any
position of the HORIZ DISPLAY switch, one of these
generators will be running. They generate the displayed
sweep in the A position of the HORIZ DISPLAY switch and
the B portion of a display in the remaining positions. The B
TIME/DIV switch (DLY’D SWEEP knob) selects the sweep
rate for these generators. One generator provides the 0.5
second through 1 microsecond sweep rates, while the
other generator provides the 0.5 microsecond through
0.01 microsecond sweep rates.
Either the “Main” Gate or the Delayed Gate can initiate
sweep generation by the Non-Delaying Sweep
Generators. When the HORIZ DISPLAY switch is in the A
position and the TIME/DIV knobs are locked, a positive
voltage is applied to the emitter of Q992, through R922 and
Q1062. Q992 is forward biased, and the “Main” Gate is
passed on to the Non-Delaying Sweep Generators
through CR922 and CR971 or CR1001. In all the other
positions of the HORIZ DISPLAY switch and when the
TIME/DIV knobs are unlocked, a negative voltage is
applied to the emitter of Q922 to reverse bias Q992 and
prevent the “Main” Gate from reaching the generators.
Now, only the “B” Gate can initiate sweep action in the
Non-Delaying Sweep Generators.
Non-Delaying Sweep Generator Differences
Basically the Non-Delaying Sweep Generators operate
in the same manner as the Delaying Sweep Generator.
The “fast” generator (Q1004, Q1010, Q1014, and Q1018)
has only one timing capacitance (the parallel combination
of C1008 and C1009). The capacitance is variable to
achieve precise timing accuracy. Timing resistors are
selected by the B TIME/DIV switch to provide the fastest
six sweep speeds listed on the front panel.
Q988 and Q1018 are Sweep Start Amplifiers and
establish the DC level starting points for the sweeps. The
“slow” generator (Q974, Q980, Q984, Q988, and Q972)
has an additional emitter follower (Q972). This emitter
follower increases the current-gain of the loop to speed up
the retrace time of the generator (determined by the time
required to discharge the timing capacitor).
Mixed Mode Operation
Normally, Q1086 is an emitter follower with a fixed dc
level at its base established by R1094 and R1095. The fixed
level at the emitter of Q1086, in turn, is applied to the bases
of Q1018 and Q968 through CR1017 and CR987 respec-
tively. This sets the quiescent current flow through Q988
and Q1018 to establish the dc level starting points for the
sweeps as previously explained. However, when the
HORIZ DISPLAY switch is in the MIX position, the fixed
level at the base of Q1086 is replaced by the sawtooth
voltage waveform being generated by the Delaying Sweep
Generator. Now, the dc level starting point of the Non-
Delaying Generator that is running is constantly being
changed by the Delaying Sweep sawtooth until the
Delaying Sweep runs down to a voltage determined by the
setting of the DELAY TIME POSITION control. At this
time, one of the disconnect transistors (Q974 in the “slow”
Non-Delaying Generator, or Q1004 in the “fast” Non-
Delaying Generator, depending on the settings of the
TIME/DIV controls) is turned off, allowing the appropriate
Non-Delaying Generator to begin a ramp waveform
determined by the setting of B DLY’D control. The output
waveform from the Non-Delaying Sweep Generator that is
running will be a composite sawtooth waveform with the
first and last parts occurring at a rate determined by the
Delaying Sweep Generator (last part blanked out of CRT
display) and the middle part occurring at a rate deter-
mined by one of the Non-Delaying Sweep Generators.
Non-Delaying Sweep End Difference Amplifier
Q1044 and Q1034 are connected as a voltage com-
“B” Gate Amplifier
parator, and generate the same sort of logic pulses as the
Logic Comparator in the Delaying Sweep Generator
Q996 is the “B” Gate Amplifier stage. The negative-
circuit. The positive-going pulse at the collector of Q1034
going waveform from the Sweep Logic circuit is applied to
signals the end of the Non-Delaying Sweep, and the
the base of Q996. The amplified and inverted waveform at
negative-going pulse at the collector of Q1044 blanks the
the collector of Q996 is applied to the Non-Delaying
display at the end of the Non-Delaying Sweep. However,
Sweep Generators through CR996 and CR971 or CR1001
the logic pulses from this comparator are not always
to initiate sweep generation.
allowed to pass to the Sweep and Z-Axis Logic circuits.
3-19
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