Keysight N8976B

156 Keysight NFA Series Noise Figure Analyzers Service Guide
RF Section Troubleshooting (N8973B, 74B, 75B Analyzers)
Troubleshooting
5. Input Attenuator B Control Logic Verification
Press AMPTD, Attenuation, Mech Atten, 6 dB and verify the 6 dB Step LED
DS17 is illuminated. Enter the input attenuation settings found in Table 4-4
and verify the proper LED's illuminate on the Front End Troubleshooting board
according to Table 4-4.
Set the input attenuator back to 10 dB by pressing AMPTD, Attenuation, Mech
Atten, 10 dB on the analyzer. If the LED's illuminate correctly, the switch
control logic for the input attenuators 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 4-4 Attenuator B Logic
Attenuator Setting (dB) DS20
30 dB
Step LED
DS19
20 dB
Step LED
DS18
10 dB
Step LED
DS17
6 dB
Step LED
10 X
16 X X
20 X
30 X
40 X X
50 X X
60 X X X
66 XXXX