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S W E E P
+ OVER SWEEP
If noise is used as a video trigger and the TRIGGER LEVEL control is properly set, the
minimum dead time period, the noise signal trigger will be present. If a video trigger does not
occur (TRIGGER LEVEL control set fully CW or CCW), then the Auto Trigger circuitry will
generate a trigger approximately every 25 ms. TP2 and TP5 will have the relationship shown
in Figure l-2. If the voltage at U13 pin 3 is much less than U13 pin 2, then TP3 will be
approximately +4 V. If the opposite is true, the waveforms at TP3 and TP2 will be the same.
If no fast sweep is occurring, check TP5 first. If the voltage is greater than +2.6 V, the most
likely failure would be in the Fast Sweep Control circuitry. Refer to the circuit description for
operation of this functional block. An open Discharge Switch would also cause TP5 to remain
greater than +2.6 V for all fast sweep times.
If TP5 is 0 f20 mV dc and no fast sweeps occur, the Fast Sweep Control circuitry should be
examined. Other defective components that would cause the same indications are Q13 and
The Sweep Trigger circuitry can be tested by tracing the trigger signals through U16 to pin
13 of UlO. Try triggering first, as this is the simplest source. A TTL signal at the power line
frequency should be present at TP3. U7 pin 12 and the FAST SWP ENABLE line should
both be high. Also check for proper trigger signals at TP3.
Sweep times in the fast sweep time mode, being difficult to verify, require a precisely
modulated RF source. One quick troubleshooting method is to disconnect the white @ cable
from A3A9J2 and connect it between A3A2J2 and A3A2Jl. This routes a 200 kHz test
6 A3Al
I
1 0 ms
F R E Q U E N C Y S P A N : 0 H z
S W E E P T I M E : 2 ms
Figure 2. Fast Sweep Line Trigger Waveforms
7 ms
v
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