Keysight Technologies X Series Service Manual page 254

Front End Control Troubleshooting
A15 Front End Control Assembly Troubleshooting
Figure 6-9 Connector Detail
The voltage should be ~21.5 VDC steady state at this point. When you switch
from Standard Path to uW Preselector Bypass, you should see a negative going
pulse to 0 VDC on the oscilloscope for ~15 mS before the voltage returns to
~21.5 VDC steady state. The oscilloscope triggering may need to be adjusted
to see the negative going pulse. This can be tested on both connectors that
contain the green wire.
254 Keysight N9010A EXA Service Guide