Agilent Technologies E4440A, Service Manual

Page: 55 / 436

Chapter 2 55
Overall Troubleshooting
Isolating the faulty assembly when the displayed amplitude is incorrect or the instrument fails
a gain related Auto Align test
If the signal level is correct:
The signal path from the A10 3
rd
Converter 2
nd
IF Amp to the
output of the A7 Digital IF is good.
The problem is somewhere between the input to the A14 Input
attenuator and the 2
nd
IF Amp on the A10 3
rd
Converter.
a. Press the green
Preset
key to turn off the 321.4 MHz internal
calibrator and restore normal instrument operation.
b. Turn on the internal 50 MHz calibrator or inject a 50 MHz,
−
25 dBm signal into the PSA RF input. Tune the PSA to
50 MHz. The PSA block diagram shows expected power levels
at the inputs and outputs of the assembly blocks. Follow the
instrument set-up instructions in the upper right hand corner
of the block diagram.
c. Measure the input signals and output signals of each circuit
assembly between the Front Panel input connector and 3
rd
Converter until you find the wrong signal level.
If the signal level is not correct
The signal path from the A10 3
rd
Converter 2
nd
IF Amp to the
output of the A7 Digital IF is faulty.
a. Press the green
Preset
key to turn off the 321.4 MHz internal
calibrator and restore normal instrument operation.
b. Turn on the internal 50 MHz calibrator or inject a 50 MHz,
−
25 dBm signal into the PSA RF input. Tune the PSA to
50 MHz. The PSA block diagram shows expected power levels
at the inputs and outputs of the assembly blocks. Follow the
instrument set-up instructions in the upper right hand corner
of the block diagram.
c. Measure the input signals and output signals of each circuit
assembly between the input to the 3
rd
Converter and test point
TP5 on the A7 Digital IF.