54 Chapter 2
Overall Troubleshooting
Isolating the faulty assembly when the displayed amplitude is incorrect or the instrument fails
a gain related Auto Align test
run using an external source rather than the internal 50 MHz
calibrator.
Press
System, Alignments, Align All Now to perform the Auto Align
routine.
If the Auto Align now passes:
The internal 50 MHz calibrator signal is faulty.
Suspect the cable that connects the 3
rd
Converter to the
Attenuator cal switch.
Suspect the 3
rd
Converter calibrator circuit. Measure 3
rd
Converter at J7.
Suspect the cal switch on the A14 attenuator.
Suspect the Reference Assy is not providing the 50 MHz signal
(difficult to verify since the signal goes through the mother
board.)
If the Auto Align does not pass:
Suspect gain problem in at least the low band (3 Hz to 3.05 GHz)
signal path. However, you need to check the highband path (3.06
to 6 GHz) to determine if the problem is also there. To do this
connect a 5 GHz, −25 dBm signal to the PSA input and tune the
PSA to 5 GHz. If the problem appears in high band also, you can
assume assemblies COMMON to both paths could be the source
of the problem.
2. Determine if the problem is between the RF input connector and a
portion of the 3
rd
Converter, or if the problem is somewhere between
the A10 3
rd
Converter and A7 Digital IF output.
Instruments with Basic Mode (Option B7J or Option 122 or 140)
To perform this test on analyzers with Basic Mode, which is most
analyzers, you will turn on the 321.4 MHz calibrator on the 3
rd
Converter and switch it into the signal path. When you do this, the
signal path is from the 2
nd
IF amp on the 3
rd
Converter to the output
of the Digital IF. This test assumes the 321.4 MHz internal
calibrator is good.
Press the green
Preset key (and factory preset if required). Press
Mode, Basic, Input/Output, Input Port, choose IF Align, then press Peak
Search
. The signal level should be about −23 to −27 dBm. Notice that
you did not need to set the PSA center frequency because the PSA
front end is bypassed.
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