Agilent Technologies 8590 Series Service Manual page 233

The DAC value is unique for each analyzer. The
self-calibration routine adjusts this value based on the amplitude of
the digitized video signal on the processor/video board assembly. The
calibration routine makes this adjustment while calibrating the
reference level at top screen.
After running the
DAC has a typical value of 165 with a range of 130 to 185. The
higher the DAC value, the greater the output from the A9 third
converter assembly.
4. Check the signal path from the analyzer input to the output of the
A14 log amplifier assembly. Refer to
located in Chapter 5
5. 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.
• If the REF LVL CAL DAC value is 255 and the input to the A9
third converter assembly is above the test limit, suspect a low
gain problem in the IF section. Continue with the troubleshooting
procedures in "IF Power-Level Measurement."
• If the REF LVL CAL DAC value is 0 and the input to the A9 third
converter assembly is nominal, suspect a high gain problem in
the IF section. Continue with the troubleshooting procedures in
"IF Power-Level Measurement."
• If the REF LVL CAL DAC value is 255 and the input to the A9
third converter is below the test limit, suspect a low gain problem
in the RF/LO sections. Continue with the next step.
• If the REF LVL CAL DAC value is 0 and the input to the A9 third
converter is above the test limit, suspect a high gain problem in
the RF section. Continue with the next step.
6. Set up the analyzer as shown in "Instrument Settings for RF
Power-Level Measurement" in this chapter.
7. Isolate the failure to an RF or LO assembly by performing the RF
Power-Level Measurements procedure in
Once the problem has been isolated to one of the four sections, use
standard troubleshooting methods to locate the source of the failure.
The following failure symptoms are examples to help isolate a failure to
either the RF, LO, IF, or Video sections.
Chapter 4
Isolating an RF, LO, IF, or Video Problem
calibration routine, the REF LVL CAL
CAL AMPTD
"IF Power-Level Measurement"
of this guide.
Troubleshooting the Analyzer
CAL AMPTD
Chapter 6 of this guide.
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