Rohde and Schwarz SME 03 Repair - Page 1
Forum section: electronics / repair

author: _rushin_or_draggin_
author_rank: Regular Contributor
timestamp: August 23, 2024, 06:50:30 pm
content: Hey all,I recently got a R&S SME 03 that is in need of some serious repair. To start, the display has a ton of black lines through it. I am tempted to strip it down and reseat it on the strip as replacements seem to be $500 (unless someone here knows of another that will work). Secondly, there are sections in the 0-1.5 GHz card that do not modulate (I get the dreaded ALC 110 error). Anything above 1.5 GHz has no output at all along with the ALC 110 error. Self-calibration of the output level fails. There are just a ton of things wrong with it. I'm just wondering if there is anyone on here that has experience working on these (especially the screen right now). I have already replaced the transistor that is prone to losing gain and they seemed to fix it slightly, but it still has issues.Thanks in advance

author: edpalmer42
author_rank: Super Contributor
timestamp: August 23, 2024, 10:55:35 pm
content: Quote from: _rushin_or_draggin_ on August 23, 2024, 06:50:30 pmHave you found the R&S group at groups.io?https://groups.io/g/Rohde-and-SchwarzThere are some useful messages & files there. There is also an incomplete service manual which may be helpful.QuoteMine has a slightly related problem. Above levels of ~+10 dBm one side of the output clips.You may have a more serious problem with the 'Output Module 3 GHz', part #1038.8140. It includes a proprietary DPDT RF switch. For frequencies below 1.5 GHz, the entire board is switched out. Above 1.5 GHz, the board is switched in and doubles the frequency. So at 2 Hz above 1.5 GHz, the input to the Output Module is 750.000 001 MHz.The board is located directly behind the front panel. To investigate further, you normally need an official extender card. I found that I was able to remove the cover from the board, move the front panel off to the side while leaving it connected, and probe the Output Module with my LeCroy 9384L 1 GHz scope. If the switch looks good, you can continue probing further into the card.I confirmed that the RF switch in mine is partly shot, but I decided not to mess with it because I can work around the problem.QuoteThe same display is used in multiple R&S units so you might be able to find a cheap parts unit. I think that the CMD-80 is one such unit, although it looks like the price for that model has jumped recently.

author: _rushin_or_draggin_
author_rank: Regular Contributor
timestamp: August 24, 2024, 02:56:06 am
content: Thanks for the groups.io link, I am currently scanning it. I got the service manual for my unit and am reading through some of the testing portions. Playing around with the SME some more, I find that I DO in fact get output when the frequency is >1.5 GHz, but only when I have modulation turned on. Whenever the modulation is turned off I get the 110 Output Unleveled error. Without doing much digging, I am guessing that is an issue in a gain section somewhere? I am going to have to make my own extension cables for the 64 (I think) pin headers along with the coax (I saw somewhere on here I think someone had asked what the connections were, I will have to see if I can find the thread).As for the screen, I see that I can get the exact replacement for a cool $500 USD, which I am not too excited about. My goal is to get this unit working as best as I can before I even consider buying a new screen, and before that I am going to try reseating it on the zebra strip to see if that fixes it. Until I get this unit working though I am not touching a thing on the display.Anyway, does having the unit display the 110 Output Unleveled error only when modulation is turned off on higher frequencies ring a bell at all? For the most part, modulation off on frequencies <1.5 GHz seems to work, except for a section around 23.2-35.1 MHz, which seems like an odd value to me. Once modulation is on it is fine. I'm hoping the 3GHz card isn't dead, because it is showing some life atleast.

author: _rushin_or_draggin_
author_rank: Regular Contributor
timestamp: August 24, 2024, 03:31:05 am
content: I also want to state again that performing the LEV PRESET calibration results in an error. My guess is I need to get that fixed first. I see in the service manual that when the calibration table is lost (which is the case with mine) that the 110 error can occur. I do see that the output level correction should be performed once the modules have been repaired but as I do not have the hardware/software to do that, I am at a loss on that. One step at a time I suppose.

author: edpalmer42
author_rank: Super Contributor
timestamp: August 24, 2024, 05:16:25 am
content: I can't really be much more help.My unit also had a dead battery. I replaced it and performed the calibrations listed in Section 2.11.8 of the Operating Manual. Everything just worked - even with the output clipping. So, other than exploring that clipping, I didn't really have to dig into the beast.I do remember that bare displays were available on ebay, but they seem to have disappeared. FYI, the part number is in the service manual. Make sure you're looking at the manual for your particular front panel version.I've attached a couple of documents that talk about the display and repairs including the 110 error. They were translated from German by an online service that's listed in the corner of the first page. Hope there's something useful there.

author: drhex
author_rank: Regular Contributor
timestamp: August 24, 2024, 08:20:56 am
content: Calibration software is available K04BB but you need a specific GPIB setup plus a supported power meter/head.

author: KeBeNe
author_rank: Regular Contributor
timestamp: September 24, 2024, 11:49:47 am
content: Hi,A few words about the errors.A different internal signal path is used for AM.The Level Preset Cal will always fail as long as the target level is not reached at the output detector.To delete the old user calibration, hold down Preset when switching on, I also recommend this to search for errors.The level drop by 30Mhz may be due to the revision of the A10, there was a non-public service bulletin for this. (see attachment)The calibration software is of no use to you, as long as the device has errors, it will not start, as the stored errors are retrieved and if a setpoint is not reached, it is immediately cancelled with an error message, which is also correct.

author: _rushin_or_draggin_
author_rank: Regular Contributor
timestamp: September 24, 2024, 03:57:06 pm
content: Update: I have removed A11 and redirected the signal path from A10 to the attenuators. Starting the unit while holding preset results in it identifying as a SME02. Running all internal calibrations it calibrated without any errors. Checking against other equipment, it seems to be working perfectly as a SME02. Reinstalling A11 without pressing the preset button results in the unit identifying as an SME03 but still without errors. Once I go above 1.5 GHz I get the ALC 110 error. I have made extension coax and a back plane connector extension and can power the unit up with A11 still connected but physically out of the unit. I’m planning on tracing the signal path through the board and try and see where it’s getting lost. That and also reading the service manual for A11.Any other ideas at this point? Or anything I should check in particular?