Rohde schwarz CMS50  - Page 1
Forum section: electronics / repair

author: JasperNL
author_rank: Contributor
timestamp: September 25, 2014, 05:29:48 pm
content: Hi all,I have the opportunity to buy a Rohde Schwarz CMS50 radio test set from my employer. Before I make the purchase I would like to know if the device is fully functional. I am testing and figuring out all the functions. I’m a bit confused with the following results:First image:Connected a 434Mhz antenna to the high power INPUT 1 jack. Creating a RF signal with my remote car key. The device measures -33dBm.Second image:Connected a 434Mhz antenna to the low power INPUT 2 jack. Creating a RF signal with my remote car key. The device measures -72dBm.Why is there a 39dB difference between the channels? Is the input 2 damaged and reading low? Is there a setting that can cause this difference? Or replace user?Second situation:INPUT 1 jack is connected to INPUT 2 jack with a 50E coax. Device is operating in tracking mode.First image: output power: 0dBmFirst image: output power: -10dBmFirst image: output power: -20dBmFirst image: output power: -40dBmI would expect that the measured power is about the same as the source power. But the measured power is about 55dBm lower. Consistently for the different output power settings.Why?Thanks in advance!Greetings JasperNetherlands

author: dave_k
author_rank: Frequent Contributor
timestamp: September 26, 2014, 11:05:02 am
content: Start by setting the input attenuation to manual ..

author: JasperNL
author_rank: Contributor
timestamp: September 26, 2014, 12:34:41 pm
content: With the INPUT 1 jack (image 1) the RF attenuation is set manual to 0dBm.With the INPUT 2 jack (image 2) the manual RF attenuation can't be selected by the user. AUTO is the default when using INPUT 2.This is also the case when in tracking mode. AUTO is the default.

author: JasperNL
author_rank: Contributor
timestamp: September 28, 2014, 07:05:03 am
content: I received an email from an EEVblog member/visitor. He owns the CMS54. More options and higher spec but comparable.He did the following test on his unit.Source: 0dBm 10MHz with 30dB attenuator on the input.Both inputs measures the same power level. What you would expect.My CMS50 input 2 is definitely damaged

author: tautech
author_rank: Super Contributor
timestamp: September 28, 2014, 07:22:59 am
content: It seems you might get it very cheap then?

author: JasperNL
author_rank: Contributor
timestamp: October 26, 2014, 05:58:51 pm
content: I think i found the problemThe first amplifier in the input 2 path is faulty. When i bypass this amplifier the signal level goes up.It is N317. Does anybody know what type it is?

author: tautech
author_rank: Super Contributor
timestamp: October 26, 2014, 06:17:55 pm
content: Have you checked all the passive components close by?In a recent thread for a SA fix a fusible resistor was open that was incorporated in the design to protect the input stages.Lets hope somebody can recognise your 4 terminal smd marked "1" device.

author: rastro
author_rank: Frequent Contributor
timestamp: October 27, 2014, 01:16:15 am
content: Possible candidates:http://www.minicircuits.com/pdfs/ERA-1+.pdfhttp://www.minicircuits.com/pdfs/MAR-1+.pdf(probably closer to 1GHZ range)On the mmic amps it may be helpful to look what voltage and bias resistors are being used and then compare it to the recommended supply voltage/bias resistors in the data sheet.

author: Unknown
author_rank: Unknown
timestamp: October 27, 2014, 09:52:49 am
content: First amplifier input 2 (red in the CMS52 service manual) 1NA03184

author: KJDS
author_rank: Super Contributor
timestamp: October 27, 2014, 10:46:45 am
content: Quote from: Marcel on October 27, 2014, 09:52:49 amI'd guess that should be INA03184

author: JasperNL
author_rank: Contributor
timestamp: October 28, 2014, 06:51:55 pm
content: Marcel send me some schematics of the CMS52 input board. Thanks for thatUnfortunately is does not match my CMS50 input board. But I think is worth a try to replace the faulty part with an INA03184.

author: JasperNL
author_rank: Contributor
timestamp: November 03, 2014, 07:44:03 pm
content: Received two INA03184. First thing i noticed is that the package is twice as small as the original one. It is not the correct part but I tried it anyway.The signal level is now 10dB higher than it is supposed to be. So the MMIC was definitely faulty.The INA has 25dB gain. That means the original one had about 15dB gain.The search continues....

author: Fraser
author_rank: Super Contributor
timestamp: November 03, 2014, 08:33:51 pm
content: From memory one of the Minicircuits MAR series had something close to 15dB gain.The MAR-1 looks a possibilityWhen I see a 4 pin package like that with a single number between 1 and 8 on it, I think MAR or ERA series. MAR predates ERA and is a larger package.I have attached datasheets and a useful document that details the markings etc.

author: KJDS
author_rank: Super Contributor
timestamp: November 03, 2014, 09:25:57 pm
content: One minor word of warning, and my memory is a little hazy on the details, but once upon a time the original MAR series amplifiers were GaAs devices. IIRC, it was Avantek who upgraded their line to an InGaP process and used this upgraded process to make amplifiers with the same specification. Whilst the spec stayed the same, the gain, instead of falling gracefully above the max spec'd frequency carried on halfway to daylight. When used as replacements in many circuits they oscillated.To keep things obvious to all, the new advanced devices were given the name of the previous ones and the old devices were renamed. I wonder if any of the other RF guys on here remember the details more clearly than I. The change took place around 2001 I believe.

author: Fraser
author_rank: Super Contributor
timestamp: November 03, 2014, 09:52:30 pm
content: @KJDS,Interesting information. Thank youI have used MAR series amplifiers for many years because they are stated as unconditionally stable (except for the MAR-8) and tend to be well behaved in most situations. I was not aware of the change that you mention but it is definitely something I will watch out for in future.I personally love the small MMIC gain blocks as they are so easy to use and provide very respectable performance for their cost. I have used better MMIC amplifiers with a flatter response but the cost increases significantly with better flatness of response.They are certainly better than the old Philips OM series hybrid amplifiers that I used to use.Aurora

author: rastro
author_rank: Frequent Contributor
timestamp: November 03, 2014, 11:47:37 pm
content: Aurora,Thanks for posting "MMICs markings.pdf" - this is a really handy cross-reference/identification sheet.

author: JasperNL
author_rank: Contributor
timestamp: December 15, 2014, 05:25:43 pm
content: Still no luck finding the service manual for the CMS50.Does anybody have any idea where i can find or buy the service manual?

author: merox
author_rank: Regular Contributor
timestamp: December 16, 2014, 06:05:21 pm
content: Quote from: JasperNL on December 15, 2014, 05:25:43 pmHave you already tried calling Rhode & Schwarz for a manual? I've read many repair stories onhttp://www.amplifier.cd(german site) and the support was always described as very helpful. Sometimes they even switch you through to the former developer of the defective hardware and they seem to have been always very willing to help in troubleshooting.

author: JasperNL
author_rank: Contributor
timestamp: December 18, 2014, 11:55:19 am
content: Thanks merox for the tip.I emailed R&S about the identification of the the part. They responded the next day with the partnumber:MSA-0104Never thought company's like R&S support the hobbyist with their old gear.Rohde & Schwarz THANKS!!

author: merox
author_rank: Regular Contributor
timestamp: December 18, 2014, 04:45:52 pm
content: Quote from: JasperNL on December 18, 2014, 11:55:19 amWell, as we say in germany: "It doesn't hurt to ask!" (Fragen kostet nichts!)And it seems the part is cheaply available at ebay.

author: Fraser
author_rank: Super Contributor
timestamp: December 18, 2014, 08:00:23 pm
content: MSA0104 is equivalent in spec to a Mini-Circuits MAR1. The MMIC shown in your picture has the markings of a MAR-1 component. No issue which is used but interesting all the sameAurora

author: sorenkir
author_rank: Regular Contributor
timestamp: December 19, 2014, 10:37:36 am
content: Hi,I had 2 MMICs "fixed" by simply heating them (quite a lot, in an attempt of desoldering them): one MAR-8 (in a Rohde Schwarz SMX) and a MWA-230 (in a Wavetek 5155A).I don't know why (I don't think it was a solder joint problem), but maybe worth a try ?Michel.

author: JasperNL
author_rank: Contributor
timestamp: December 25, 2014, 09:13:13 am
content: Replaced the MMIC wih MSA0104 and its working againLevels are now correct. Maybe it needs calibration but for now i am very happy.Thanks for all your input.

author: tautech
author_rank: Super Contributor
timestamp: December 25, 2014, 09:26:28 am
content: Quote from: JasperNL on December 25, 2014, 09:13:13 amMerry Christmas