| Products > Test Equipment |
| Rohde & Schwarz CMU200 |
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| richnormand:
The PSU can run OK without a load when provided with a good start signal. I do not remember a spike at start-up. There was a long thread on fixing the CMU200 PSU with lots of details on it. In particular how to start it when out of the unit for testing. It can run OK without a load. EDIT Here it is: https://www.eevblog.com/forum/repair/rohde-schwartz-universal-radio-communication-tester-cmu200-psu-issues/ I'll find it and edit this post when I do. 1) The start up spike is worrying. Can you scope it to see if it is real? 2) Check all the PSU filter electrolytics. 3) Remove all the plug-ins (over load can shut down the PSU) and also see if the front processor board boots OK and does not initiate a shutdown. 4) Mentioned above, the small fan on mine was seized. Easy to dismantle and oil. Been OK for several years now. Did the same for the main fan. Good luck with it. |
| arno:
Dear all, the CMU is back up running. I simply cleaned the PSU using flux cleaner (there was a little bit of dust on the PCBs). Also, I could already swap the HDD for a SSD. Self tests are passing. Thanks again for your help! Arno |
| _Wim_:
--- Quote from: arno on July 04, 2021, 08:16:42 pm ---Dear all, the CMU is back up running. I simply cleaned the PSU using flux cleaner (there was a little bit of dust on the PCBs). Also, I could already swap the HDD for a SSD. Self tests are passing. Thanks again for your help! Arno --- End quote --- Good news! Enjoy your unit! |
| arno:
Hi, it's me again. Re-Assembled the unit today and there is something really wrong with it on the RF side. When I send in 0 dBm it reads about -30 dBm and the generator is about 50 dB lower than it should be. Is it possible it lost all it's calibration during the repair? Is the reference somehow broken? When I run the internal loopback tests (1->4 / 2->3) / Internal RF Loop, it does not read any power at all. Thanks in advance! Arno |
| capt bullshot:
Loopback tests (1->4 / 2->3) require an external cable connection between the mentioned ports (just in case you didn't notice that). If it's only these tests that fail, I'd check the RX/TX module without the RF front end connected (remove the two hardlines from RX/TX to RF frontend) and measure directly at the RX/TX module SMA connectors. There's just a (quite convoluted) bunch of RF switches and gain blocks within the RF front end, all the basic functions of the CMU will operate with the front end disconnected, levels will be off by a few dBs. Port 3 and Port 4 have MMIC amplifiers more or less directly coupled to the connectors, these might be shot by externally applied DC or whatever, causing the external loop tests to fail. Port 1 and Port 2 will continue to work anyway, if this is the issue. |
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