Table of Contents
ADC/Interface Section
A3 Assembly Video Circuits
Variable Gain Amplifier (VGA)
Refer to function block AB of A3 Interface Assembly Schematic
Diagram (sheet 6 of 6) in the
Component Level Information
The VGA provides adjustable gain in the video path. Its nominal gain of
7 can be adjusted ±10%. U112 removes dc offset to keep U113 in its
monotonic range. (Both U112 and U113 are set to the same value.) The
DAC settings cannot be changed from the front panel.
Track and Hold
Refer to function block AC of A3 Interface Assembly Schematic
Diagram (sheet 6 of 6) in the
Component Level Information
1. Press
on the HP 8560E/EC and set the controls as follows:
PRESET
Center frequency ..................................................... 300 MHz
Span ................................................................................. 0 Hz
Detector mode ............................................................. Sample
Reference level ......................................................... −70 dBm
Log dB/division .......................................................... 2 dB/div
Sweep time ................................................................... 50 ms
2. Disconnect any signal from the spectrum analyzer input. A full scale
display of sampled noise should be present.
3. Trigger an oscilloscope on the positive going edge of HHOLD
(A3U506 pin 16).
4. The waveform at A3TP10 should be random noise with an average
level of approximately 4 V. The noise should have a flat spot in its
response while HHOLD is high, indicating proper operation of U114.
380
HP 8560 E-Series Spectrum Analyzer
.
HP 8560 E-Series Spectrum Analyzer
.
Chapter 7
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Troubleshooting
