After months of absence I just picked up my most favorite device the Rohde & Schwarz CMU200 again and it seems I will be having time to hobby in evenings of the upcoming months
as I have quite a few to repair
I know there are a lot of users on this forum with problems with the CMU200.
I have received an internal notice that a lot of these units will be on the market as a new batch of redundant material is sold. I have seen the lists so I ecpect these will be online at the usual auction sites within a few months.
Anyway back to the topic.
One of the often seen problems is apart from power supply or hanging during startup (serial number hanging) is the drop op particular band responses.
In the picture below you see an example of the output of the CMU200 checked with a spectrum analyzer
It can take weeks before you discover where this problem is comming from. Good news is that I have identified it by using the large test bench for the CMU I had made.
The problem is luckely not in any of the extremly dense soldered plugins or calibration settings but on the rather easy 1100.2500.02 unit
I have not taken time to check it on component level but 100% sure this is the cause as replacing it solved the issue.
I will spent more time on the CMU so I'm back on the forum