Rohde & Schwarz CMU200

[arno]

Hello everybody,

I bought a used CMU200 two weeks ago. Everything worked fine until yesterday. Unplugged it from mains in the morning, replugged in the afternoon, fans came up for a couple of seconds, the power LEDs were still green, not orange. I am also able to go into standby by pressing the power button for a couple of seconds, but after re-powering the fans come up for a few seconds, then turn off. I already took of the case and all LEDs on the bottom of the mainboard light up after turning the unit on, but then go off. To my understanding the issue must be somewhere else but the PSU.

Thanks in advance,
Arno

[dencyaupin]

Hello everybody! Help with troubleshooting and identify mixer board details.

[_Wim_]

Hello everybody,

I bought a used CMU200 two weeks ago. Everything worked fine until yesterday. Unplugged it from mains in the morning, replugged in the afternoon, fans came up for a couple of seconds, the power LEDs were still green, not orange. I am also able to go into standby by pressing the power button for a couple of seconds, but after re-powering the fans come up for a few seconds, then turn off. I already took of the case and all LEDs on the bottom of the mainboard light up after turning the unit on, but then go off. To my understanding the issue must be somewhere else but the PSU.

Thanks in advance,
Arno

Maybe also a keyboard related issue?

https://www.eevblog.com/forum/repair/cmu200-boot-failure-power-suplly-erratic/msg1193017/#msg1193017

[arno]

Dear Wim,
thank you for the hint. As far as I could investigate, the keyboard is not the cause.

Arno

[_Wim_]

According to your symptoms it does indeed seem a short circuit is present somewhere. So first thing to do it find the faulty module.

[_Wim_]

According to your symptoms it does indeed seem a short circuit is present somewhere. So first thing to do it find the faulty module.

Screenshot from pag 112 of this service manual: http://gotroot.ca/cmu200/RS_CMU200_CMU300_other.pdf

[arno]

Wim, thank you very much for your help, I really appreciate that. Today I had no free time to keep on the investigation but will come back asap.

Arno

[arno]

Hello everybody,

today I measured all the voltages at the test points next to the LEDs. In the moment the unit powers off, there is a huge peak on the rails of 3.3V and 6V (my multimeter [Keysight U1272A] peaked 28V). Have not yet measured with the scope. Took the whole PSU apart, but there are no visible faults at all.

Arno

[_Wim_]

Hello everybody,

today I measured all the voltages at the test points next to the LEDs. In the moment the unit powers off, there is a huge peak on the rails of 3.3V and 6V (my multimeter [Keysight U1272A] peaked 28V). Have not yet measured with the scope. Took the whole PSU apart, but there are no visible faults at all.

Arno

I would try to remove all plugin modules and see it the motherboard boots. If the rails are ok before it turns off, my guess would be this is only a turn off glitch with no actual power in it. When it boots with no plugin, reinstall one card at a time and check if it still boots with the added card.

Be sure to take pictures before removing cards, so you exactly know were everything goes when reassembling.

[Ice-Tea]

Check all flatcables on the motherboard. A half unplugged cable has ruined my day once or twice in these machines.

What I've also seen to result in startup issues: the front (computer) module has a fairly weak fan that goes bad and seizes after time. The elcos on the board dry out, behaviour becomes eratic. Often visible cap damage. Worth checking out.

[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_]

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

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.

[richnormand]

Loopback Rx/Tx tests:

I would make sure loop cables is hooked up in front (good quality cables needed)
I would check the various flat cables to the unit.
I would check the SMA lines under the mainboard are connected connecting to the Tx/Tr module and that it is well seated in the main connector.

Lots of info in this thread:
https://www.eevblog.com/forum/repair/rohde-and-schwartz-cmu200-rxtx-module-issues/

[_Wim_]

Loopback tests  (1->4 / 2->3) require an external cable connection between the mentioned ports (just in case you didn't notice that).

Indeed, but as there is quite a bit of cross-talk between the channels, this can be confusion because your actually seeing a signal, but it is just to low...

[arno]

Dear all,
thanks for so many replies. I unplugged the front RF module from the RXTX-board and connected both SMA connectors. Then, in RF1 internal loopback test, I saw around -30 dBm, but ONLY in Bd (I assume band) 5, between 2.2 and 2.7 GHz. The rest is still dead. Also, I do not see any RF power from the TX out. 

Edit: opened up the RXTX-unit. There are no visible damages, like broken caps or something, just some dust.

Thanks
Arno

[arno]

Dear all,

sorry for the long break, I was quite busy and could not work on my CMU. Luckily I found a replacement RXTX-Board and the unit is fully working, again!   

Thank you all for your help!

Arno

[richnormand]

Hi arno,
just sent you a pm.
Cheers

[Decee1]

Hello.
Anyone can help with my issue? I am getting nowhere with it..
https://www.eevblog.com/forum/rf-microwave/rs-cmu200-gpibcom-communication-problems/

[webxtor]

Hello.
Here some company sells the equipment used for mobile phones repair and I am expanding my own amateur workshop.
So now this device is on the auction and I am trying to find out the possible use of it.
As far as I understood it does not support 4g/LTE or newer networks and may thus be used only as a toy and nothing serious about the modern phones?
What is the application for it you have found nowadays?

Thanks

[capt bullshot]

The CMU200 is still useful as a spectrum analyzer (10MHz to 2.7GHz) and signal generator (up to 2.7GHz) for general use.

[CJay]

Hello.
Here some company sells the equipment used for mobile phones repair and I am expanding my own amateur workshop.
So now this device is on the auction and I am trying to find out the possible use of it.
As far as I understood it does not support 4g/LTE or newer networks and may thus be used only as a toy and nothing serious about the modern phones?
What is the application for it you have found nowadays?

Thanks

Depends what options are available on the unit you buy but the one I have is pretty useful for me.

It works as a spectrum analyser, it has dual RF signal generators, I can use it to analyse filters, antennas etc..

It also has the audio module s it's as a simple audio analyser and audio signal generator, I can also measure SINAD, Audio power and RF power with it.

 

[486dx4]

Hi - just reading the posts.  Where can one get the latest version of FreRes these days.  I did find version 4.3.1 but I do see screenshots of a version 5.x.x  The links given in the older posts do not seem to be valid anymore and searching for the application note 1ma09 on the Rohde website comes up with nothing (granted this software is old now I'd say).  If anyone happnes to have info on where to download that would be great.