Rohde Schwarz CMU200 - Page 1
Forum section: electronics / repair

author: ON4GN
author_rank: Newbie
timestamp: April 19, 2024, 04:03:14 pm
content: 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 itselfI 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-B68Someone an explanation or solution.

author: minolta
author_rank: Contributor
timestamp: April 19, 2024, 05:49:45 pm
content: 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.

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 20, 2024, 07:28:10 pm
content: Quote from: minolta on April 19, 2024, 05:49:45 pmDear 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...PSIf 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.

author: ON4GN
author_rank: Newbie
timestamp: April 22, 2024, 02:12:18 pm
content: 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 b1to 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

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 22, 2024, 03:16:53 pm
content: Quote from: ON4GN on April 22, 2024, 02:12:18 pmPlease check again all the voltages from PS.

author: ON4GN
author_rank: Newbie
timestamp: April 23, 2024, 12:43:44 pm
content: 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.

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 23, 2024, 01:44:41 pm
content: 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.

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 23, 2024, 02:50:12 pm
content: 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.

author: ON4GN
author_rank: Newbie
timestamp: April 24, 2024, 02:03:03 pm
content: 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 : ERRORI 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

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 24, 2024, 05:11:53 pm
content: Quote from: ON4GN on April 24, 2024, 02:03:03 pmNot a big problem as you have as many as two CMU. Clarify what CMU has fault level.Is it RF Output or RF Input.After simply change modules to localize the bug.PSMeantime could you make photos of B68 from both sides. Unfortunately I have no such option.

author: ON4GN
author_rank: Newbie
timestamp: April 28, 2024, 09:50:11 am
content: Hello Harry_22.Here are the photos from the CMU-B68.

author: ON4GN
author_rank: Newbie
timestamp: April 28, 2024, 09:56:45 am
content: More photos

author: Harry_22
author_rank: Frequent Contributor
timestamp: April 28, 2024, 04:26:45 pm
content: Please remove the modules 1135.5206.02 as well as 1100.2400.25 and place burned part areas in the center of photo. The burned parts are seen on both sides.

author: snickers
author_rank: Contributor
timestamp: May 06, 2024, 03:56:14 pm
content: Almoust all electrolitic capacitors in my FMR6 were blown.Now its Ok

author: Harry_22
author_rank: Frequent Contributor
timestamp: May 06, 2024, 04:23:28 pm
content: FMR controllers supply from 5.2VDC. All board capacitors are for internal low voltage convertors.I haven't seen so many blown capacitors in R&S. In major cases FMRs have BIOS malfunction.

author: snickers
author_rank: Contributor
timestamp: May 06, 2024, 05:12:43 pm
content: I think ... The problem was with the previous owner. Small FAN on FMR seems to be replaced.FAN stopped -> temp inside FMR high -> caps blownThey replaced FAN, but not capacitors.