Keysight Technologies Option 503 Service Manual page 160

RF Section Troubleshooting (RF/Microwave Analyzers)
Troubleshooting
Second LO Level Verification
The second LO signal comes from the A16 Reference Assembly and is only
used in Low Band. The second LO signal can be measured on the Front End
Assembly at A13A1J1 or the A16 Reference Assembly at A16J702. Expected
signal is 4800 MHz at +10 dBm when a low loss test cable is used and with the
measuring spectrum analyzer input attenuator set to at least 20 dB to prevent
overload.
First LO Level Verification
The first LO is the A20 YTO assembly. The first LO is phased locked by the A14
Synthesizer assembly and controlled by tuning signals from the A15 Front End
Controller.
To assure the first LO is tuned to the correct frequency and power, measure the
A13 Front End assembly at A13A1J3 when the analyzer center frequency is
50 MHz. This test port is chosen because removing cable W19 will not cause
the analyzer LO phase lock loop to unlock, which would affect the LO
frequency measurement.
The LO signal should measure 5172.5 MHz at +10 dBm ± 3 dB.
If the signal level is incorrect, measure the signal coming from the A20 YTO at
A13A1J4. In order to measure this signal and avoid an LO Unlock, you will need
to install a power splitter at A13A1J4. Connect one arm of the splitter to
A13A1J4 using a sma (m) to sma (m) adapter. Connect the input of the splitter
to W20 using the sma 90 degree adapter and short sma cable. Connect the
measuring spectrum analyzer to the other arm of the splitter. Add the loss
through the splitter arm which is 6 dB for the Keysight 11667B splitter.
The signal should be 5172.5 MHz at +10 dBm ± 3 dB
When measuring A13A1J5, Synth Out, the splitter must also be used. The
expected signal level is 5172.5 MHz at +10 dBm ± 3 dB
A13 Front End Assembly Verification
The A13 Front End assembly is shown as A13A1 and A13A2 for
troubleshooting clarification. However, A13A1 and A13A2 are not
separately replaceable. The entire A13 assembly must be replaced.
Many portions of the Front End Assembly have been verified earlier in the Low
Band troubleshooting process outlined above.
The input signal level was measured on W8 as part of the A11 Low Band
Switch verification.
The output signal level was measured at A13A1J7 during the quick check to
verify the Low Band Signal Path.
The Second LO input was tested during the Second LO Verification.
160 N9030A PXA Signal Analyzer Service Guide