Author Topic: Rohde Schwarz CMU200 Repair of analyzer level dips  (Read 1224 times)

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Offline RF_fanatic

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Rohde Schwarz CMU200 Repair of analyzer level dips
« on: March 14, 2017, 08:16:41 pm »
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
« Last Edit: March 14, 2017, 09:40:46 pm by RF_fanatic »
 

Offline RF_fanatic

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Re: Rohde Schwarz CMU200 Repair of analyzer level dips
« Reply #1 on: March 14, 2017, 08:58:55 pm »
In the picture is the responsible DIG module with the responsible plugin (red label) underneath also the same plugin in working condition
 

Offline richnormand

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Re: Rohde Schwarz CMU200 Repair of analyzer level dips
« Reply #2 on: March 14, 2017, 09:59:38 pm »
Nice to see you back :)

Hopefully you will have the time to examine that module at the component level to find out what the cause is (hardware/software) since most of us don't have access to multiple units to swap boards.
If you think of ways I could be useful please let me know.
 :box:
 

Offline RF_fanatic

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Re: Rohde Schwarz CMU200 Repair of analyzer level dips
« Reply #3 on: March 22, 2017, 09:56:37 pm »
Good to read you are also still active with the cmu 200 richnormand !

Indeed I am lucky to have multiple units and was able to make a test bench for it. Unfortunately you live far away otherwise it would be an honour to invited you to bring your unit and put it on the test bench. To check which modules are deviating.

In the past week I have tested quite a few digital modules.

With the following main conclusions regarding faults,, the % is based on : if problem exists how much is the change for it in the respective plugin:

* Hangs during initiation session (ser. nr. Not recognized)
   1100.3220.02 (28%)
   1100.2130.03 (72%)
* Level of TX to low -20dB
   1100.2130.03 (75%)
   1100.1956.04 (25%)
* Level of TX to low (endless)
   1100.2130.03 (50%)
   1100.1956.04 (50%)
* Crashes during measurement, or irregular measurement levels (flat lines etc), or very slow
   1100.3220.02 (100%)
* Bandgap dips
  1100.2500.02 (100%)
* slightly to high >5 or to low <5 over full range
  1100.2500.02 (100%)

Hope this will help some of you out there.

I have all the defective boards from the above tests but not have had time yet to repair (next focus is the Front End)
 

Offline Velund

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Re: Rohde Schwarz CMU200 Repair of analyzer level dips
« Reply #4 on: March 23, 2017, 12:20:47 am »

* slightly to high >5 or to low <5 over full range
  1100.2500.02 (100%)


Do you mean analyser levels only here, or both TX and RX side?
 

Offline RF_fanatic

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Re: Rohde Schwarz CMU200 Repair of analyzer level dips
« Reply #5 on: March 23, 2017, 07:44:51 am »
On the tx side. (but I have not checked specificly if the RX was also bad with the same unit)

Nice thing to notice was that by checking the TX side (which is the most easy part), all problematic boards had been identified.

When I all checked them afterwards for the RX levels I noticed that all remaining good TX performing boards also passed the RX test.


« Last Edit: March 23, 2017, 07:50:52 am by RF_fanatic »
 


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