170   Keysight NFA Series Noise Figure Analyzers Service Guide
RF Section Troubleshooting (N8973B, 74B, 75B Analyzers)
Troubleshooting
Disconnect cable W15 or W36 at A13J7, 322.5 MHz output on the Front End 
Assembly (1). See Figure 4-19. 
Figure 4-19  W15 or W36 Location