182 Keysight NFA Series Noise Figure Analyzers Service Guide
RF Section Troubleshooting (N8973B, 74B, 75B Analyzers)
Troubleshooting
When the input attenuation is changed from 0 dB to 2 dB, the 2 dB Step LED
DS15 should illuminate. When the input attenuation is changed from 2 dB to
4 dB, DS15 and DS16 should be illuminated as per Table 4-11.
The analyzer default setting for RF Coupling is AC mode. Verify the AC Select
LED DS14 is illuminated at this time. Set Input/Output, RF Coupling to DC.
DS14 turns off, DS11 DC Select yellow LED should illuminate. Switch the RF
Coupling back to AC. If the LED's illuminate correctly, the switch control logic
to Input Attenuator A from the A15 Front End Control Assembly is correct. If the
LED's are not illuminating as expected, the most probable cause is the A15
Front End Control Assembly.
Table 4-11 Attenuator A Logic
Attenuator Setting (dB) DS15 DS16
0
2X
4XX
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