TM 9-6625-1753-14
C2
The delayed sweep unblanking pulse (strobe) makes a brighter trace than the delaying sweep pulse.
e. The delaying sweep is automatically turned off when the delayed sweep has terminated. This action is developed as
follows: the positive gate produced at the collector of delayed sweep multivibrator Q8106 is applied to a differentiating network
consisting of R8247 and C8216. Series-coupling diode CR8202 is biased to permit only the trailing edge of the delayed
sweep gate to trigger the delaying sweep multivibrator and subsequently terminating the NDT sweep. This prevents
brightening of the sweep retrace in the STROBE position.
3-20.
Delayed-Triggered Mode (Figs. 3-18, 3-19, and 6-4)
When the DISPLAY LOGIC switch is set to TRIG DLY'D, the delayed sweep and not the delaying sweep is applied to the
horizontal deflection amplifier. The brightened sector of the display in the STROBE position will not be expanded to full
screen in the DLY'D position. The delayed-triggered sweep circuit is similar in operation to the triggered-strobe mode
described earlier, except that the strobe circuit is not activated. Automatic provision is made for shut-off of the delaying sweep
when the delayed sweep terminates. This technique permits maximum duty cycle performance in the delayed mode.
3-21.
Armed-Strobe Mode (Figs. 3-20, 3-21, and 6-4)
a. When the DISPLAY LOGIC switch is set to ARM STROBE, the delay pick-off circuit, the arming multivibrator, the
delayed sweep, and strobe circuits are activated. In the "armed" mode, the delayed sweep is triggered by a selected external-
triggering signal. All triggering signals are blocked by the armed lockout diode until a signal from the delay pick-off circuit
triggers the arming multivibrator. This action unlocks the diode and opens the trigger circuit to the delayed sweep, making it
Figure 3-17. Simplified timing diagram, triggered-strobe display.
applied to strobe circuit Q8001 and Q8002. The positive strobe signal is applied to one of the beam-gating electrodes of the
CRT. The delaying sweep unblanking gate is applied to the other beam-gating electrode.
d. The cathode-ray beam is kept turned off when a sweep is not moving the beam across the screen. When a sweep is
Figure 3-18. Delayed-triggered mode, functional block diagram.
in progress, the beam is turned on by an unblanking signal that lasts long as the sweep and then turns the beam back off after
the sweep is completed. When both the delaying and delayed sweeps are running, each produces its own unblanking signal.
3-18
