Rohde Schwarz CMU200 Repair of analyzer level dips - Page 1
Forum section: electronics / repair

author: RF_fanatic
author_rank: Regular Contributor
timestamp: March 14, 2017, 08:16:41 pm
content: 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 monthsas I have quite a few to repairI 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 analyzerIt 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 unitI 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

author: RF_fanatic
author_rank: Regular Contributor
timestamp: March 14, 2017, 08:58:55 pm
content: In the picture is the responsible DIG module with the responsible plugin (red label) underneath also the same plugin in working condition

author: richnormand
author_rank: Unknown
timestamp: March 14, 2017, 09:59:38 pm
content: Nice to see you backHopefully 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.

author: RF_fanatic
author_rank: Regular Contributor
timestamp: March 22, 2017, 09:56:37 pm
content: 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 -20dB1100.2130.03 (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 slow1100.3220.02 (100%)* Bandgap dips1100.2500.02 (100%)* slightly to high >5 or to low <5 over full range1100.2500.02 (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)

author: Velund
author_rank: Regular Contributor
timestamp: March 23, 2017, 12:20:47 am
content: Quote from: RF_fanatic on March 22, 2017, 09:56:37 pmDo you mean analyser levels only here, or both TX and RX side?

author: RF_fanatic
author_rank: Regular Contributor
timestamp: March 23, 2017, 07:44:51 am
content: 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.

author: RF_fanatic
author_rank: Regular Contributor
timestamp: December 01, 2021, 09:50:34 pm
content: After many years I have checked, repaired and sold all the CMU's I had left. I eventually even sold a hand full of units I initially wanted to keep as spare but well I needed the space for a new hobby.So my test bench has been scrapped a few weeks ago I only have a box of spare parts left but I will stop following the CMU topic.I will do some last checks with the spareparts left and will eventually list them on ebay, probably as bulk unless people here are interested.It was fun getting to know all the ins and outs of the CMU but time to move on.For some interested in parts you can drop me a message.

author: richnormand
author_rank: Unknown
timestamp: December 01, 2021, 10:19:38 pm
content: Your contributions were appreciated by a lot of people indeed.Best of luck with your new hobby and most importantly, don't forget to have fun.Cheers