Keysight Technologies X Series Service Manual page 244

Front End Control Troubleshooting
A15 Front End Control Assembly Troubleshooting
The analyzer default setting for RF Coupling is AC mode. Verify the AC Select
LED DS14 is illuminated at this time. Press Input/Output, RF Input, RF
Coupling, AC/DC to DC on the analyzer. DS14 should turn off and DS11, DC
Select LED should illuminate. Switch the RF Coupling back to AC. If the LED's
do not illuminate correctly, the most probable cause is the A15 Front End
Control Assembly.
244 Keysight N9010A EXA Service Guide