Chapter 3 75
Troubleshooting the RF Section (E4440A, E4443A, E4445A)
RF Section Description (E4440A, E4443A, E4445A)
RF Assembly Quick Check - E4440A, E4443A, E4445A
NOTE To perform the following checks, it will be necessary to remove the outer
case and the top brace. See Chapter 11 for removal procedures.
Turn the instrument on and allow it to complete its internal calibration
routines. This routine will generate error messages if the signal level is
incorrect through the system. Inject the 50 MHz, −25 dBm calibrator
signal to the RF Section by pressing
Input/Output, Input Port, Amptd Ref
(f = 50 MHz). Set the instrument to CF = 50 MHz, Span = 0 Hz, and the
input attenuator to 10 dB.
Disconnect the cable with the “3” color band from the third converter
21.4 MHz output A10J5. Connect the RF Input of another spectrum
analyzer to A10J5. A 21.4 MHz, −27 dBm ±2 dB signal should be
present.
Verifying a Faulty Front End Assembly
E4440A, E4443A, E4445A
Overall Front End
Finding a fault in the RF front end is best done by breaking the path
and monitoring the signal level and frequency with another spectrum
analyzer. The signal levels and frequencies are noted on the overall
block diagram foldout for given input conditions. In following the first
LO, breaking the signal path between the A18 YTO and the A21
SLODA, or at the Sampler Output of the SLODA, will cause an unlock
condition. This can be resolved by using a power splitter to keep the
loop complete and yet facilitate measurement. In doing this, the
measured signal level due to loss of the splitter must be taken into
account.
Since most RF section assemblies are expensive, a suspected faulty
assembly should be verified by checking bias voltages and input signals
before replacing them. This is best accomplished by improving
accessibility of the test points and nodes on the A13 Front End
assembly by using the extender boards and cables supplied in the
Service Kit E4440-60090. For troubleshooting the RF Section, use the
following pieces supplied in the kit:
A13 Front End Driver Extender E4440-60049
A13J12 Bias Board E4440-60041
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