TM 9-6625-1753-14
screen, falls on either side of the trace (horizontally). To correct this effect, we adjust STROBE PATT CORR variable resistor
b. Triggered-delayed.
R8005 (zone C15) and trimmer capacitor C8004 in the collector circuit of strobe amplifier Q8002.
(1) In this mode, the bright segment of the CRT display in the triggered-strobe mode is expanded to cover the full
(15) Let's briefly summarize the detailed description of the triggered-strobe mode, using the waveforms in figure 3-9.
screen. The amount of expansion is proportional to the ratio of the normal sweep rate to the delayed sweep rate.
The first waveform shows the output of the normal sawtooth generator that goes to the horizontal deflection amplifier and the
comparator stage in the delay trigger pick-off circuit. After comparing the normal sawtooth with a fixed voltage determined by
(2) With the DELAY LOGIC switch set at TRIG-DLY'D, the delayed sawtooth generator output, rather than the normal
the DELAY VERNIER control, the comparator produces a squared output (waveform 2) which is a result of the tunnel diode
sawtooth generator output, is sent to the horizontal deflection amplifier. The circuitry described in paragraph a above for the
action. Waveform 3 shows the inverted-differentiated output of the differentiating amplifier that is applied to the delayed-
triggered-strobe mode is also used in the triggered-delayed mode. The circuits operate in exactly the same way except that in
sweep gate multivibrator after it passes through a pulse transformer and a diode.
this mode the strobe circuit is deactivated and has no effect on the CRT display.
(3) In addition, when the delayed sweep is completed, the normal sweep is automatically terminated. This increases
its duty cycle to the optimum value. As an example, suppose the normal sweep is 2 seconds long; the delayed sweep is 50
milliseconds; and the time (delay) until the delayed sweep starts is 50 milliseconds, as shown in figure 3-10 (a) and (b). You
can see, if the normal sweep isn't terminated at the completion of the delayed sweep, we will have to wait approximately 2
seconds (1950 milliseconds) before we can again observe a display on the CRT screen. This is undesirable since it doesn't
permit continuous display of the signal on the CRT screen.
(4) To make sure the display is continuous, the positive output of the delayed-sweep gate multivibrator triggers the
normal-sweep gate multivibrator to its initial operating state. The positive-gate output of the delayed-seep gate multivibrator is
differentiated by RC network C8216, R8217 (zone A9). Diode CR8202 passes only the negative pulse (representing the
trailing edge of the positive gate and the end of the delayed sweep), which triggers the normal-sweep gate multivibrator to its
initial operating state.
Figure 3-9. Triggered-strobe mode waveforms.
(16) The negative-gate output of the delayed-sweep gate multivibrator, shown in waveform 4, activates the Miller
integrator circuit, producing a sawtooth signal (waveform 5) that is terminated at the DISPLAY LOGIC switch. At the same
time, the positive-gate output of the delayed-sweep gate multivibrator is applied to the strobe circuit. This circuit produces a
strobe pulse that has the same duration as the delayed sweep and is shown by waveform 6. One of the CRT beam gate
plates receives the strobe pulse.
Figure 3-10. Comparison of normal sweep to delayed sweep.
(17) Waveform 7 illustrates the resultant output of the unblanking amplifiers after they receive the positive gates from
c. Armed-strobe.
the normal- and delayed-sweep gate multivibrators. This signal, after passing through an emitter follower, is applied to the
other CRT beam gate plate. During the time the beam gate plates are at the same potential, the CRT presents a bright
(1) In this mode the delayed sweep doesn't start at the end of the selected delay interval until a trigger pulse via the
display. In the interval when the difference between the deflection plate potentials is some intermediate value (below cutoff)
triggering circuitry (par. 3-12) is applied to the delayed sweep circuitry. The trigger signal can be either the input to the
the CRT display is dimmer.
oscilloscope (dual trace plug-in output), or a trigger signal from an external source. Setting the DISPLAY LOGIC switch to
ARMSTROBE activates all the circuitry described in paragraphs a and b above with the addition of the armed multivibrator
(18) To make sure the retrace isn't displayed, the positive-gate output of the normal-sweep gate multivibrator is
circuit (zone C7). The armed multivibrator prevents premature triggering of the delayed-sweep gate multivibrator.
differentiated and applied to the delayed-sweep gate multivibrator. The negative pulse of the differentiated signal (waveform
8), representing the trailing edge of the positive gate, triggers the delayed-sweep gate multivibrator, which in turn, deactivates
(2) You will recall that the setting of DELAY VERNIER control R8617 (zone B11) determines the delay interval, the
the delayed sawtooth generator. In addition, the strobe circuit no longer receives the positive gate, and therefore, a strobe
time between the start of the normal sweep and the generation of a gate by the comparator circuit. You will also recall that
pulse isn't generated. With the delayed-sweep gate multivibrator in its initial operating state and the strobe pulse not being
this output is differentiated by Q8604, R8621, and C8611 and is applied to transformer T8601. Diode CR8104 passes the
generated, the potential difference between the beam gate plates is such that it prevents the electron beam from reaching the
CRT screen.
3-12
