396 Keysight NFA Series Noise Figure Analyzers Service Guide
Assembly Replacement Procedures
Instrument Outer Case
3. Refer to Figure 15-5. Using the T-20 driver, remove the four screws 
including washers (1) that hold the rear bumpers (2) (two on each side) 
in place.
Figure 15-5  Option PRC Instrument Outer Case Removal
4. Pull the instrument cover (3) off towards the rear of the instrument.