TM 11-6625-2735-14-1
MIX or A INTEN positions of the HORIZ DISPLAY switch,
some additive unblinking is accomplished to slightly
increase the intensity of the B portion of the display. In
these positions of the switch, –8 volts is connected to the
cathodes of CR693 and CR694 through R692. Now, when
the Z-Axis signal from the collector of Q826 steps negative
at the beginning of the B portion of the display, CR693 is
made to conduct less current, which makes a slight
amount of additional unblinking current available to the
Z-Axis Amplifier through CR694 and R692.
Delaying Sweep Latch Circuit
Q788, Q794, and Q796 form the Delaying Sweep Latch
Circuit. The circuit function is used during the three
delayed sweep modes of operation that the instrument is
capable of (MIX, A INTEN, and B DLY’D). Q938A, in the
Delay Pickoff Comparator of the Delaying Sweep
Generator, is the current source for the emitters of Q794
and Q796. Prior to the end of the delay time selected by the
A TIME/DIV switch and DELAY TIME POSITION control,
Q938A is off, thereby causing both Q794 and Q796 to be
off also. The base level of Q794 sits at a more negative level
than does the base of Q796 so that when Q938A turns on,
at the delay pickoff point, Q794 will turn on and Q796 will
remain off. The resultant positive movement at the
collector of Q794 is connected to the B Trigger TD Reset
Circuit.
The end-of-sweep pulse from the Non-Delaying Sweep
Generators connects to the emitter of Q788. When this
pulse steps positive at the end of a delayed sweep, Q788
turns off and the current through R788 pulls the base of
Q794 positive. This turns off Q794 and causes Q796 to turn
on. The circuit remains in this state until the Delaying
Sweep Generator ends its sweep and resets the Delay
Pickoff Comparator. In the B ENDS A position of the A
TRIG HOLDOFF control,
+5 volts is connected to R798.
This enables the diode gate composed of CR799 and
CR592 Now, when the end-of-sweep pulse signals the
end of a delayed sweep, the positive movement at the
collector of Q796 is connected to the base of Q594 and
ends the delayed sweep Instead of waiting until the end of
the delaying sweep. This mode of operation gives the
fastest possible sweep repetition rate when operating in
the delayed sweep mode.
B Trigger TD Reset Circuit
Q790 and Q792 are connected as a Schmitt Trigger and
form the B Trigger TD Reset Circuit. At all times other than
when the Non-Delaying Sweep Generators are running,
Q790 is on, which holds the trigger tunnel diodes in the B
Trigger Generator circuit in their LO states. At the end of
the delay time selected by the A TIME/DIV switch and
DELAY TIME POSITION control, the positive movement
at the collector of Q794 turns on Q792 and causes Q790 to
turn off. The tunnel diodes in the B Trigger Generator are
capable of being biased into their HI states. Also, if the B
Triggering SOURCE switch is in the STARTS AFTER
DELAY TIME position, the negative movement at the
collector of Q792 reverse biases CR811, letting the –8volt
supply pull down on the base of Q804 in the Delayed Gate
Comparator This turns on Q804 and causes Q802 to turn
off, which initiates a delayed sweep.
Main Sweep Holdoff Gate and Delayed Sweep Over-
ride Amplifier
During the interval of the main gate, Q798 functions as
a holdoff gate and is biased off to provide a forward bias on
Q1002 (Q1002 is located on diagram 9). This turns on
Q1002, discharges the holdoff capacitors and maintains a
current path to keep the capacitors discharged.
During the delayed sweep, Q798 functions as an
override amplifier. It is possible, with the right combina-
tion of control settings, to achieve a delayed sweep
presentation where the delayed sweep would normally
want to continue running after the end of the delaying
sweep. For instance, if the TIME/DIV controls are set only
1 or 2 ranges apart and the DELAY TIME POSITION
control is set to a 8.50 setting. Under these conditions the
delaying sweep end-of-sweep pulse occurs before the
delayed sweep end-of-pulse. The positive movement on
the collector of Q588 at the time of the delaying sweep
end-of-sweep pulse turns Q798 on. The negative move-
ment on the collector of Q798 pulls down on the collectors
of Q794 and Q796, through CR793 and CR792 respective-
ly, which in turn pulls down on the base of Q792. This turns
off Q792 and causes Q790 to turn on, which resets the B
Trigger Tunnel Diodes to their LO states, thereby ter-
minating the delayed sweep.
A +GATE And B +GATE Amplifiers
Q584 and Q824 are the A +GATE and B +GATE
amplifiers respectively. They provide the +GATE output
signals available at the instrument rear panel. These
output gate signals are positive-going rectangular
waveforms, approximately 5 volts in amplitude, coincident
with their respective sweep waveforms.
LOW LINE Indicator Circuit
Q1492, Q1498, and their associated circuitry monitor
the unregulated voltage in the +50 volt supply and provide
a visual indication (via the LOW LINE indicator on the
front panel) when the applied line voltage falls below the
lower regulating Iimit selected by the Regulating Range
Selector assembly Q1482 provides operating power to
the CRT graticule lights that is adjustable via the SCALE
ILLUM control R1480
3-15
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