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Rohde & Schwarz CMU200

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luc-on7kz:
Thanks Rudi,
having watching the video but it has notting telling me what i not know,
The service manual is poor no detailed schematics or even a more detailed blockdiagram or the place on the PCB is not to find
A lookup to the RX/TX board has also no visual issues except a small corrosion on one of the SWA filters, but where to find these parts and second problem placing these parts, I have some experience with SMD but these are just a little to high, I will not destroy the working parts.   :scared:
Any tip will be appreciated
thanks into advance
Luc On7KZ

_Wim_:

--- Quote from: luc-on7kz on June 30, 2023, 05:31:35 am ---The generator and spectrum analyzer is only functioned to 2.2Ghz, readed spectrum levels are correct but not higher than 2.2Ghz

--- End quote ---

Are you sure it is both the generator AND spectrum analyzer that are limited to 2.2GHz? I would expect it is ONLY the analyzer part. If that is the case, I would not expect it is the same corrosion issue with the filters as I had, as the filter used for >2.2GHz is also used below 1.2GHz which is working fine.

My first suspect would be a damaged RF switch (SW-239 from Maccom). Try to measure these in circuit (there a quite a few of them) and check if one of them is measuring very different with a multimeter. This could be an indication of a damaged switch.

A better (but much more work) approach is to check for each switch if a signal is seen on port A and port B when sweeping over the entire range. This however requires to solder test wires to each of the RF-switch A&B ports to be able to measure them when the unit is powered on. So I would first try to measure with a multimeter on the board itself to see if no obvious suspect is detected.

These boards have big copper planes which make it hard to remove components. So do be careful with a hot air gun as you have to add a lot of heat. As easier way in my opinion is to cut the legs of the part you want to remove with a fine cutter, and then remove leg by leg with a soldering iron. This is off course only possible if you are already sure the component in broken.

_Wim_:

--- Quote from: _Wim_ on July 01, 2023, 08:03:49 am ---My first suspect would be a damaged RF switch (SW-239 from Maccom). Try to measure these in circuit (there a quite a few of them) and check if one of them is measuring very different with a multimeter. This could be an indication of a damaged switch.

--- End quote ---

Have a look at this post: https://www.eevblog.com/forum/repair/cmu200-rx-level-issue-failed-loop-test/msg3916070/#msg3916070

If you board looks similar, I would expect one of the two RF switches above mixer 1A & 1B might be broken. If your board looks different, it might be a good idea to try and reverse engineer like I did based on the block diagram. These boards are fairly easy to follow where the signals go, but it still takes several hours to complete...

luc-on7kz:
Hello _Wim,
Reading and learning a lot here on these forum, your tips are great
Its so that both RX an TX fail above 2.2Ghz
The spectrum is working perfect till these frequentie, even better than my siglent SAA3021 (31) and these have i tested whit a 1Ghz signal from my R&D SMG
In the TX part i have 3dB less than it must be and these on all the outputs RF1, RF2 and RF3 i suppose somewhere a attenuator fault or ??
The search is on, I hope that it will be possible to make the CMU300 be working 100%
If that is OK than I will looking for the B41 module
greetings Luc

_Wim_:

--- Quote from: luc-on7kz on July 01, 2023, 01:37:53 pm ---Its so that both RX an TX fail above 2.2Ghz

--- End quote ---

Hi Luc, in that case it is more likely that something common is broken (and thus not an RF-switch). It could be that "LO0" is used both for the RX and TX part. In my diagram I labeled LO1A and LO1B, but probably R&S labels them LO0 and LO1. As you get a tune error on LO0, this would make sense. So I would check with your SAA3021 if you get an LO signal on both mixers first.

Edit: it is very well possible the LO frequency is out of range for the SAA3021, a power meter might be a better option to check if an LO is present

Edit2: just reread my old post, the LO of mixer 1A was shared between RX and TX, so I would check this one first

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