CMU200 Problems - Page 1
Forum section: electronics / beginners

author: soulkeeper1357
author_rank: Newbie
timestamp: May 07, 2020, 05:51:31 am
content: [ Specified attachment is not available ] [ Specified attachment is not available ]I am way below beginnerIt has always been my interest with electronics to the point of buying test equipment even not knowing to use it but gradually learning by experimentation.Not so long ago, I came across a CMU200, 1100.0008.10 roughly 150USD and I bought it for the purpose of testing HAM radios.As I started it there were issues on the CMU200.1. CMOS Battery - Dead (Already replaced with a new one)2. Keypads buttons are not working (Report Button, 1,2,3) and missing 2 below the display. (Going to order the with Aliexpress for keyboard contacts and Ebay for the buttons)( I had to take a video of the individual test just to review it)Internal Test conducted was either Passed or Within Parameter for the following1. REF Test2. DIG Test3. AUXTX Selftest4. System Selftest5. FE Selftest6. RXTX 1 Selftest7. Linkhandler Selftest8. Hardware data VerificationArea of Concern:1. I was expecting a 50w max input on RF1 but got 2w input max2. Errors with Internal AuxTx Loop Path 1 (Pic 1)3. 1->4/3->2 Loop Path 1 *Led indicators at the Frontend were working properly3.1 Loop 1->4 All Failed (Pic 2)3.2 Loop 3->2 All Failed (Pic 3)4. Internal RF Loop Path 1 - Failed4.1 1->11205 Bd3 to 2200 Bd4, -33dBm - No Measurement (Pic 4)1205 Bd3 to 2200 Bd4, -53dBm - No Measurement (Pic 5)1205 Bd3 to 2200 Bd4, -73dBm - No Measurement (Pic 6)4.2 2 -> 21205 Bd3 to 1610 Bd4, -16dBm - No Measurement (Pic 7)1710 Bd4 to 1940 Bd4, -16dBm - Exceeded (Pic 7)2070 Bd4 to 2200 Bd4, -16dBm - No Measurement (Pic 7)1205 Bd3 to 1610 Bd4, -36dBm - No Measurement (Pic1710 Bd4 to 1940 Bd4, -36dBm - Exceeded (Pic2070 Bd4 to 2200 Bd4, - 36dBm - No Measurement (Pic1205 Bd3 to 1610 Bd4, -56dBm - No Measurement (Pic 9)1710 Bd4 to 2070 Bd4, -56dBm - Exceeded (Pic 9)2200 Bd4, -56dBm - No Measurement (Pic 9)5. Reference Frequency NOT LockedAction Taken1. Tested Reference Voltage (X221) for 5v2. Tested Voltages and it was with in parameters (Pic 10)I read some of the posting about the CMU200 likeRXTX problem -https://www.eevblog.com/forum/repair/rohde-and-schwartz-cmu200-rxtx-module-issues/msg1020780/#msg1020780PSU Issue -https://www.eevblog.com/forum/repair/rohde-schwartz-universal-radio-communication-tester-cmu200-psu-issues/Surely this is not PSU problem since voltage are within specified value and no sign of abnormal power activity.With the information stated above I am seeking assistance for the following question.1. What is causing the problems with the unit and where should I start checking? (Loop Path, Reference Frequency Not Locked)2. If I wanted to change the RF frontend to accommodate 50w what part number should I be looking for? (I am also considering attenuator for this to lessen the expense)Factors that are to be considered1. I live in a 3rd world country and sourcing small parts for replacement might be more expensive due to non-availability rather than buy used modules.2. Due to the pandemic, cargo shipments are delayed.With all that being said, I am reaching out to the Gurus for help and guidance.

author: Ice-Tea
author_rank: Super Contributor
timestamp: May 07, 2020, 06:23:01 am
content: 1) Keypad issues: there's a copper tape connecting the two layers of the keypad foil. It oxidized and peels easiliy. Apply new copper tape, remove oxidization or punch through it and it should work.2) 50W input: both options exist, the 50W is actively cooled. The 2W allows more additional rf options, I believe3) ref frequency unlocked: in the "connect control" tab you can choose whether to take the 10MHz reference internally or externally. Set it to internal4) The rest of your issues probably lies in the RXTX board (maybe you'll see improvements after switching to internal ref, dunno). Essentially, your shit out of luck. As you can see, there are several frequency ranges that correspond to 3 mixers. All stitched together with oodles of rf witches and a generous helping of configurable attenuators. Not saying it's impossible to fix (on my long to do list) but it looks like you have more than one problem and spare parts are expensive. Example: you can buy the actual mixer IC but it will set you back 100$ or so. Unless your The Signal Path and have access to his lab, this may be a lost cause.

author: soulkeeper1357
author_rank: Newbie
timestamp: May 07, 2020, 06:50:24 am
content: Quote from: Ice-Tea on May 07, 2020, 06:23:01 amI forgot to state that it has a CMU-B12 and it was set at Internal ReferenceQuote from: Ice-Tea on May 07, 2020, 06:23:01 amSeem the problem is intertwined, and with the CMUB12 installed do i start with the RXTX Board?what could be the modules due for replacement on this case of I want it up and running? (If I was not to consider buying used rig.)

author: richnormand
author_rank: Unknown
timestamp: May 07, 2020, 06:21:40 pm
content: Good thing the PSU voltages are OK.Good thing you changed the CMOS battery. While in there make sure the small computer and display fan is working properly (mine was seized).I would concentrate first in getting the keys fixed or at least not stuck in the "pushed" position.Next the "freq not locked" A) internal setting (already mentioned) B) From a cold start you might have to wait 15-20min for the B12 to stabilize and lock. C) the B12 module might be defective.If the B12 is "defective": A) is it detected on boot? B) remove the module and reinsert it (possible bad contact) C) remove entirely and boot (this should force the CMU200 to use the internal oscillator and see if you get the same message.The B12 and B11 options are detected automatically at boot and listed if present.RxTx issues. Remove and reinsert the modules (note the coax connectors on the backplane underneath before doing so.If you want to get in the TxRx you will need a lot of patience and equipment (like a second SA and a good scope in addition to a DMM.Before getting in there fix the ref unlocked issue.Mine has the 2W module. It is a bit of work to change to the 50W an depending on the setup you might loose some functions.There is a "maintenance manual" available for installing modules. Reference in the threads you mentioned.Best of luck with it.

author: soulkeeper1357
author_rank: Newbie
timestamp: May 10, 2020, 02:23:11 am
content: Hello richnormand,Your post is great guide for me, I started from there in checking the CMU200Quote from: richnormand on May 07, 2020, 06:21:40 pmThe unit can detect the B12, I removed and reinsert but the same error came out.I will try removing the B12 and see what happens.What could be the problem if when B12 is removed to force the unit to use the internal oscillator but still return to "Frequency Not Locked"?Quote from: richnormand on May 07, 2020, 06:21:40 pmI removed and re inserted RXTX module but same errors came up. Going in the board is a 20% option, It will take time and sourcing components will cost me in relation to shipping and I lacked other required equipment.I would try to check with RXTX boards for sale online to replaced it, it will come out cheaper.On the Frontend module, if ever I get to fix this error ill stick with the 2w and use the 20db 50w attenuator.

author: Ice-Tea
author_rank: Super Contributor
timestamp: May 10, 2020, 09:26:31 am
content: - Double check that the reference is indeed on internal (connect control). Post a screenshot for us to verify if you want to make sure.- Don't buy a RXTX board online *unless* the vendor can prove it comes from a unit that passes internal and external loop tests. Loop test failures are common, and I wouldn't break up a working CMU with a good RXTX board. Would make a *lot* more sense and would be a lot easier to replace whatever is faulty than to part it out.

author: soulkeeper1357
author_rank: Newbie
timestamp: May 13, 2020, 10:29:21 am
content: Quote from: Ice-Tea on May 10, 2020, 09:26:31 amCurrently I have to wait for the keypad foil. The CMU does not want to start, stays in green indicator. I think this have something to do with the foil being cleaned, it used to boot and work and now the power button is not responding.Quote from: Ice-Tea on May 10, 2020, 09:26:31 amThat part I did not think about, thank you for the insight. Without the CMU200 booting up and no parts yet, I might just try to test the RXTX board parts individually for the meantime.

author: Ice-Tea
author_rank: Super Contributor
timestamp: May 13, 2020, 10:32:25 am
content: The power button is also on the foil so that makes sense

author: oh4mvh
author_rank: Newbie
timestamp: December 26, 2020, 03:22:34 pm
content: Regarding RXTX board. My CMU200 is looking similar to yours in these internal tests i.e. no measurement value on certain frequencies. when I was trying to repair it, CMU200 was standing on its left side. In that position I saw few times tests were succesfull, but when I tried to move the RXTX board slightly, measurements failed as well as when CMU200 was standing in normal position. I was pretty sure there is failure in connectors but I have not found it neither reprocedure it anymore. I even used connector cleaner liquid in the motherboard connector without seeing any difference.What I don't understand is that e.g. in spectrum mode and with a second signal generator, I generate CW signal connected to port 4 and run the test manually changing the signal level in external signal generator, I see the test reads it approximately correct level. I tested on several frequencies also. And in CMU200 spectrum analyser mode I can see the external signal generator signal level over the supported frequency range approximately on the same level. So the RX paths looks like it works.I have also done measurement with external spectrum analyser to see the signal out from port 1 that it is present and approximately on the same signal level. So for mee it looks like TX path works also.So, I have started to suspect the motherboard connector provides control signals to perform the internal test measurements, and if there is something wrong in the control signals, the internal test measurement fails. I have no schematics to verify which pins provides the signal to take a look to them. Is there anybody who could have some hint on that?