Step Attenuator driver circuit for Rohde & Schwarz FSEM / FSEB / FSEA problems

[hafrse]

Hello,

I have an issue when stepping the input  attenuator in my FSEM , it seems that the operating system crashes/hangs and I need to restart the analyzer. some king of surge or noise when switching to different step  is generated and hangs the entire system. 
Any experience which board  and parts/area in that board  the attenuator dirver circuit are located?

Thanks!