258 Chapter5
Troubleshooting the IF Section
IF Power-Level Measurement
To inject a signal at the output of the A11
bandwidth filter assembly
Inject a 21.4 MHz signal at the output of the A11 bandwidth filter
assembly with the following procedure. Refer to Figure 9-1 while
performing this procedure.
1. Remove the A11 bandwidth filter assembly.
2. Insert the IF test board in the A11 assembly slot.
3. Connect a synthesizer/level generator to the J2 input connector on
the IF test board. The test board injects the signal at A15J8 pin 22.
4. Set the signal source for 21.4 MHz at +4 dBm. This signal level
provides +10 dBm at the input to the A14 log amplifier assembly and
simulates a top-screen signal.
5. Check for the following nominal signal outputs.
•A−10 dBm at the AUX IF OUTPUT connector on the rear panel.
Refer to measurement point C on Figure 9-1.
Use an active probe to make the measurement. If a 50 Ω analyzer
is used, an additional 6 dB drop in signal level results. (The AUX
IF OUTPUT has a 50 Ω output impedance.)
• One volt at the AUX VIDEO OUTPUT connector on the rear
panel (measurement point B). A voltage divider on the A15
motherboard reduces the uncorrected 2 volt video signal
(AUX_VIDEO) to a 1 volt output.
• A signal at the top graticule line and a marker reading of
approximately 0 dBm.
Use
CORRECT ON OFF to observe the magnitude of video offsets that the
A16 assembly is currently using to correct the signal position at
top-screen. Refer to Chapter 13, “Softkey Descriptions” for more
information about
CORRECT ON OFF.
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