CMU200

[Eyecue]

I have a CMU200 spectrum analyzer that wont pass the self test.  Further self testing shows the 8 volt supply is not correct in the RXTX unit.  The motherboard LEDS show the PSU is fine for 8 volt supply.  Any ideas or common points of failure inside the RXTX  card?

[Ice-Tea]

Not really, but I can offer pictures

[Alfons]

Are there any abnormalities in operation?

[richnormand]

Just saw your post Eyecue.
I also had issues with voltages on my RxTx in my CMU200.

Look at the fourth pix on the first post for the location on the pass transistors for the voltage regulation on the board.
https://www.eevblog.com/forum/repair/rohde-and-schwartz-cmu200-rxtx-module-issues/msg1032907/#msg1032907
You will notice that one of them has been removed (the bad one!) in the photo.

After fixing that it did not pass self test and that was traced to a bad coupling cap between the switching stages (later posts in that thread). I made extensions for the SMA connectors to the RxTx module and removed the RF fingers to the side rails. This sped up partially removing and reinserting the board multiple times.
You really need a SA if you want to troubleshoot that board for RF issues. Finally managed to get it going but it took a while.

Best of luck with it.

PS: although the LEDs are lit for the 8V rail on the motherboard check them at the test points. There is a thread with pinouts of several connectors prior to my RxTx thread.
https://www.eevblog.com/forum/repair/rohde-schwartz-universal-radio-communication-tester-cmu200-psu-issues/msg954718/#msg954718

[Ice-Tea]

Hi Richard,

JUst wanted to thank you for pointing out that thread. I wasn't aware it existed. I have a number of bad RXTX units, with errors ranging from marginal fails to missing bands to nothing at all so that thread is a true goldmine.

Thanks!

[Eyecue]

Richard,
Thanks for the reply! Mine does not look like yours.

[Eyecue]

Thanks for the reply.  The calibration comes into question when the self test wont pass.  I had to replace the CMOS battery in the front panel which led to some other issues but I got those taken care of.