396 Chapter8
ADC/Interface Section
A3 Assembly Video Circuits
6. If the output of latch A3U102 is not correct, trigger an oscilloscope
on LLOG_STB (U102 pin 9) and monitor U102 pin 1 and other latch
inputs while changing the video bandwidth.
7. If the inputs are incorrect, troubleshoot the analog bus. Correct
inputs with bad outputs indicate a faulty U102.
8. Check that the outputs of A3U111A, A3U111B, and A3U107A/B/C/D
are correct for their inputs. The outputs should be high with
noninverting inputs higher than the +1.4 V threshold voltage. If a
voltage drop is noticed across these components, suspect A3CR109 or
A3Q317B. Since no dc current flows through any of the series
resistances or FETS (drain to source), no voltage drops should occur.
9. To return the spectrum analyzer to automatic sweep, press
SWEEP, SWEEP CONT SGL or PRESET.
Video Filter Buffer Amplifier
Refer to function block W of A3 Interface Assembly Schematic Diagram
(sheet 5 of 6) in the
8560 E-Series Spectrum Analyzer Component Level
Information.
The video filter buffer amplifier provides outputs for video trigger,
positive and negative peak detectors, and the analog zero-span (sweeps
<30 ms). The zero-span video output is terminated in 500 ohms on the
A2 Controller assembly. The amplifier is a high-input-impedance buffer
amplifier with a gain of one when properly terminated.
Table 8-6 A3U102 Latch Outputs
Video BW Pin 2 Pin 5 Pin 7 Pin 10 Pin 12 Pin 15
300 Hz H L L L L L
1 kHz L L L L L H
3 kHz L H L L L L
10 kHzLLLL H L
30 kHz H L H L L L
100 kHz L L H L L H
300 kHz L H H L L L
1 MHz L L H L H L
3 MHzLLLH L L
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