Chapter 4 235
Troubleshooting the Analyzer
Isolating an RF, LO, IF, or Video Problem
The analyzer may also fail the displayed average noise performance
verification test.
1. Check the REF LVL CAL DAC value using
DISPLAY CAL DATA as
described in “Using the Internal Service-Diagnostic Routines.” This
type of problem causes the DAC value to be close to the 255
maximum.
2. Measure the 321.4 MHz input to the A9 third converter assembly by
connecting the CAL OUT to the INPUT 50Ω with a BNC cable.
75 Ω input only: Connect the CAL OUT to the INPUT 75Ω with the
75 Ω BNC cable.
Then, disconnect the W9 cable assembly from the third converter
and measure at the cable output.
The 321.4 MHz input typically measures between −36 and −39 dBm
with zero input attenuation.
3. Check the signal path from the analyzer input to the output of the
A14 log amplifier assembly. Refer to “IF Power-Level Measurement”
located in Chapter 5 of this service guide.
If the displayed signal amplitude appears too
high
This problem is caused by high gain somewhere along the RF or IF
signal path. The displayed CAL OUT signal appears to have an
amplitude greater than −20 dBm. The excessive gain causes a
calibration error that makes the CAL OUT signal appear higher than
normal.
The
CAL AMPTD self-calibration routine may not fail.
• Check for a REF LVL CAL DAC value of 0 using
DISPLAY CAL DATA
as described in “Using the Internal Service-Diagnostic Routines.”
The values in the ERR column are 0.00 or have a negative value.
• Measure the 321.4 MHz input to the A9 third converter assembly by
connecting the CAL OUT to the INPUT 50Ω with a BNC cable.
75 Ω input only: Connect the CAL OUT to the INPUT 75Ω with the
75 Ω BNC cable.
Then, disconnect the W9 cable assembly from the third converter
and measure at the cable output.
The 321.4 MHz input typically measures between −36 and −39 dBm
with zero input attenuation.
• Check the signal path from the analyzer input to the output of the
A14 log amplifier assembly. Refer to “IF Power-Level Measurement”
located in Chapter 5 of this service guide.
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