R&S CMU200 - buying guide - Page 1
Forum section: electronics / testgear

author: YU7C
author_rank: Regular Contributor
timestamp: August 05, 2019, 07:03:02 pm
content: Hi,I am considering to buy CMU200 and wonder which should I ask seller (if they are willing) to do, before I meke final decition.As all modern instrument suposed that it have a selftest.Which series should be avoided?Is there variants in processors, memory,...?Also I noticed v14 in some hardware option, but not sure what is that mean?Thanks,Vojislav

author: Bicurico
author_rank: Super Contributor
timestamp: August 05, 2019, 09:36:58 pm
content: The common problems with CMU200/CRTU are, to my knowledge:1) Broken PSU: easy to check - does it turn on/off ok? If not, don' think it is just a fuse. These PSU's are rather complex and you need to know how to repair switching PSU's. Good thing is that they turn up on the market from time to time at 100-200 Euro.2) Broken TXRX board: most common issue is selftest not passed due to some values being out of spec. These can often be found at 100-200 Euro at eBay, too.3) Broken Frontend-Module: these are harder to figure out. If the input signal is too low, missing or no signal output - then you might have a broken frontend. These can be repaired. Often there is just one tiny amplifier IC broken. You can find a thread here on this forum explaining how to replace it. BUT BEWARE: it involves desoldering a component made of Berilium Oxide, which is highly toxic - this module has a warning sticker because of this. If you don't know what you are doing spare yourself the trouble...4) However, the same symptoms can come from a broken digital board. If that is the case you are out of luck, because these are REALLY hard to get!5) Broken CPU board: can be bought for 200-300 Euro at eBay sometimes. Not much to repair, as all components are SMD and hard/impossible to obtain. Except for the memory SDIMM.So yes - there is a risk. Most good units come in Europe at around 1000-1200 Euro. If you think of it, you might be better off with a brand new Siglent SSA3021X...Unless you buy the CMU200 at a really good deal. Even better, get a second unit for spare parts!Otherwise, if you can test the unit, just run all selftest options. If there is no fault in either test - pay 1.000 Euro if the Audioanalyser option is there (hardware option). If there are some RXTX values out of spec, pay 500 Euro. If there are real issues, buy for 300 Euro as spare.Note that nowadays all software options can be unlocked with a keygen. Get a loaded CMU200 with as much hardware options as possible. For spectrum and signal generation no options are required at all. The audio analyser is a nice option, though.Regards,Vitor

author: YU7C
author_rank: Regular Contributor
timestamp: August 06, 2019, 11:43:04 am
content: How to perform selftest when is marked with OFF?EDIT: SOLVED!

author: YU7C
author_rank: Regular Contributor
timestamp: August 06, 2019, 12:06:31 pm
content: Here are result of ST I got from (honest and friendly) seller:

author: Bicurico
author_rank: Super Contributor
timestamp: August 06, 2019, 04:46:23 pm
content: You probably have a broken Frontend Module and/or TXRX-Board.Read this thread:https://www.eevblog.com/forum/repair/rohde-and-schwartz-cmu200-rxtx-module-issues/I would not pay more than 300 Euro for such a device.Regards,Vitor

author: YU7C
author_rank: Regular Contributor
timestamp: August 06, 2019, 06:36:10 pm
content: And that was a price.I got another offer for instrument w/o any selftest fail for $600.Tomorrow i will get list of option and make final decision.Thanks,Vojislav

author: YU7C
author_rank: Regular Contributor
timestamp: August 26, 2019, 07:17:16 pm
content: Hi,just received one nice looking CMU200.I am impressed with design and ergonomic. Just how the instrument has to look!Now issues.I knew in advance that instrument has an internal loop issue, but i take a risk that I'll able to repair. I have other SG&SA that could help me to trace fault(s).However I didn't expect that it has a keyboard issue. Five hotkeys (left to right 1,2,3,4,7) dont work, Other keys including escape work fine. Not sure how an electronic scanned keys, but it sound like mechanical issue not electronic.Internal loop test fail, other test pass including:Internal AUX TX loopPath1,Internal AUX TX loopPath2,Internal AUX TXW loopPath1,Internal AUX TXW loopPath2,but i don't know what above tests mean?Also I noticed that SA receive some signal from from air with 1m wire as antenna.It's difficuld to do other test w/o hotkey in fuction, so it will be first task repairing or repacement keys.Thanks,Vojislav

author: Bicurico
author_rank: Super Contributor
timestamp: August 26, 2019, 09:26:28 pm
content: Errors in the Loop Path are normally due to a fault in the RF frontend module. Also, you will probably notice that the Input/Output signal on at least one port is about -20dB too low...Faulty keys are due to a broken keyboard mat - keypad, which is made out of rubber. In my opinion these are impossible to repair as we are taking about a flexible rubber/plastic sheet where one conducting trace has been interrupted/broken.Sometimes you see these keypads being sold on eBay.What you can do is attach an external PS/2 keyboard. The faulty keys are mapped to the keyboard. You need to test which is which, though.As I said before. Get another 1-2 broken units to assemble a fully working unit.Regards,Vitor

author: YU7C
author_rank: Regular Contributor
timestamp: August 27, 2019, 06:25:04 am
content: Hi,My doesn't have PS/2 connector, but two USB.I have connected USB keyboard and the Instrument react on some keys, ENTER, Arrows, Escape,... but i could't find mapping for hotkeys.Also I found in bios, that it could enable a mouse, but it didn't show on the screen.Thanks,Vojislav

author: ps
author_rank: Regular Contributor
timestamp: August 27, 2019, 05:50:47 pm
content: The keyboard consists of a rubber mat wit carbon pills and a foil with conductive ink traces. The carbon pill is pressed against the traces, closing the contact. Primary failure mode is electromigration, causing one key to stick and block a row. The secondary failure mode is broken tracks. Tracks can be repaired with conductive ink, shorts can be fixed by carefully scraping. Ebay auctionhttps://www.ebay.de/itm/293192600733(not mine) includes some pictures of the keyboard foil.Scancode mapping is as follows:left softkeys: 10/Q, 11/W, 12/E, 13/R, 14/T, 15/Y, 16/U, 17/I, 18/Oright softkeys: 1E/A, 1F/S, 20/D, 21/F, 22/G, 23/H, 24/J, 25/K, 26/Llower softkeys: 3B/F1, 3C/F2, 3D/F3, 3E/F4, 3F/F5, 40/F6, 41/F7, 42/F8, 0C/-control group:0E/<--, 52/NumIns31/N, 30/B2F/V, 2E/C2C/Z, 2D/Xfuncton group: 19/P, 1A/[, 1B/]system group: 1B/\, 28/', 27/;number block:08/7, 09/8, 0A/9, 86/F1205/4, 06/5, 07/6, 85/F1102/1, 03/2, 04/3, 44/F100B/0, 34/., 35//, 43/F901/ESC, 1C/Enter, 0F/Tabcursor block:4B/left, 48/up, 4D/right, 50/downNote that the CMU's front module computer is a generic PC that runs MS-DOS. You can connect everything to the USB that fits, but without a proper MS-DOS device driver nothing will be recognized. For file management, you can install Volkov Commander (or Norton Commander). With PS/2 mouse emulation turned on in the BIOS and a PS/2 mouse driver in CONFIG.SYS, this will accept a mouse. However, the CMU software does not support it.Patrick

author: Ice-Tea
author_rank: Super Contributor
timestamp: August 27, 2019, 06:26:19 pm
content: Actually, the primary failure mode of the front keys is the fact that there's a conductive tape connecting front/back GND of the two layer foil. Replacing that tends to solve things

author: YU7C
author_rank: Regular Contributor
timestamp: August 27, 2019, 07:47:31 pm
content: Today I opened the Instrument, and briefly checked a foil but didn't find nothing obviously wrong, so i assembled it again. End of foil cabe is somewhere deep in the main board enclosure, and today is not a day for that.Most probably I am going to buy Chinese copy of foil from ebay.Also noticed that instrument has aux frontend.Vojislav

author: YU7C
author_rank: Regular Contributor
timestamp: August 29, 2019, 03:54:39 pm
content: Now move to repair section.https://www.eevblog.com/forum/repair/repairing-cmu200/msg2651073/#msg2651073