Rohde Schwarz CMU200

[ON4GN]

I have two CMU200with the same problem:
They start normal if I remove the CMU-B68, but with the module the power switch stay orange.
I opened te CMU-B68 and find a bad capacitor:
In both CMU-B68 is the same capacitor short, I wonder what cause this.
I think they are short by overvoltage, there are some spwer circuits in the module itself
I checked te voltages from the power supple and they seems to be OK.
On de separete connector to the CMU-B68 ( two red and two black wires ) I measure on both red wires +5 Volt.
I can't find a schematic from the CMU-B68
Someone an explanation or solution.

[minolta]

I have repaired CMU200 several times with different faults. The worst of them was overvoltage. It was because of wrong multiturn poti on PCB of PSU (wrong contact inside). This is terrible design of PSU- - with bad contact in poti there is maximum voltage near double! Designed by some school?
These DELTA PSU are crazy. In all are very bad capacitors. Changing of them - almost dead approx 25 capacitors - are very very bad work, impossible to desolder etc... primary side is heavy coated, so measuring or change something is terrible. Realy, I am afraid next CMU for repair bacause next PSU will be necessary to refurbish.

[Harry_22]

I have repaired CMU200 several times with different faults. ...
... In all are very bad capacitors. Changing of them - almost dead approx 25 capacitors

Dear Minolta,
it sounds very strange. I have fixed a lot PS-es (PLUS Typ:SN250) but this is tiny compared to how many of them were installed by R&S. No one broken capacitor has been found. Only Stand By circuit malfunction and PFC.
May be you mean TDK Lambda Vega 450? Just the reverse side is covered with a thick layer of varnish. But it has only 1-2 capacitors to change.

@ON4GN, please correct the company name to "Rohde...

PS
If the faults are the same in different devices, this indicates that the wrong parts were used. Remove them and check that the short is gone.
Typically, a thermal imager is used to detect shorts in power circuits.

[ON4GN]

Hello,
I removed all the capacitors in the power supply (34 pieces ), they looks all normal: Capacity and ESR !!!
I will order new to replace them, I still have a second supply from the other.
@ Harry_22:
All the components are original !!!
If I start the CMU without the CMU-B68 the startup is normal, and afterwards I have the normal screen on the SMU200.
I do see during startup there is no CMU-B68 module installed.
I don't think it is a power supply problem, all the voltages or good, I started to test the power supply out of the CMU200 at first with a 820 Ohm resistor from b1
to ground to be shure it start normal and it did.
It would be nice to have the schematic from the CMU-B68.
I did remove the bad capacitor on the CMU-B68 to see what happens and to measure the voltage on it, but the capacitor next to it immediately starts to smoke 

[Harry_22]

I did remove the bad capacitor on the CMU-B68 to see what happens and to measure the voltage on it, but the capacitor next to it immediately starts to smoke 

Please check again all the voltages from PS.

[ON4GN]

I checked the voltages again and they are all normal.
But I tested without the CMU-B68 and I can use the CMU200 as a spectrum analyser and the RF generator is OK.
That is actualy all I need.

[Harry_22]

Did you checked both CMU200 voltages? Seems that you have problem only in one CMU but somebody interchanged B68 option. That is why you have double malfunction.

[Harry_22]

Do you have the cable connection with PS mentioned as 1149.9596 (pls see the document)?
Could you attach the connection photo from both sides.

[ON4GN]

I checked both CMU voltages and the are the same.
The CMU-B68 are not interchanged !!!!
I gues that both CMU-B68 are irrearable, the reason for the bad caps will be probably too high voltage on some way generated into the CMU-B68.
This will demaged some other components on that PCB too, without a decent schematic it will be inpossible to find out wat is wrong.
But as I said before I can use the CMU200 without CMU-B68.

I tested the spectum analyser and RF generator and both are working.
But the " Internal RF Loop Selftest " is not OK : ERROR 
I did connect RF2 ( as output ) to RF1 (as input)
Level Tx -10dB give me -25dB on the analyser screen.  A loss from -15 db  ??
I can solve this by putting RF 1 to +15.0dB but that is not the right way.
That is my next problem now