Chapter 5 261
Troubleshooting the IF Section
IF Power-Level Measurement
To check IF section gain control
Table 5-2 lists the changes in IF Section gain that alter the displayed
signal position when the reference level is changed in increments as
small as 1 dB. The control voltages from the A7 analog interface
assembly that change the gain of specific IF assemblies are provided in
Table 5-3, Table 5-4, and Table 5-5.
When the reference level is changed, the A16 assembly performs two
step-gain functions that change the position of the displayed signal.
Refer to Table 5-2 for the reference levels where the A16 assembly
changes the signal position in increments of 10 dB. When a
reference-level change of less than 1 dB is required, the A16 assembly
makes a corresponding change in the signal position. These changes in
signal position are made by mathematically offsetting the digitized
video signal on the A16 assembly.
The A16 assembly also makes amplitude error corrections to improve
instrument performance. The reference-level changes and
error-correction functions are a combined mathematical offset of the
digitized video signal. This makes it difficult to distinguish which offset
is contributing to a change in displayed signal level when the reference
level is changed. Disable the error corrections by setting
CORRECT ON OFF to OFF.
Refer to “Troubleshooting the A15 Motherboard Assembly” in this
chapter when tracing control lines in the IF section
The entries in Table 5-2 are valid after pressing the following keys.
PRESET
CAL
More 1 of 3
CORRECT ON OFF (OFF)
Be sure that the input attenuator setting remains at 10 dB.
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