Electronics > Repair

Rohde & Schwarz SMIQ03B with Error 110 Output unleveled; IQMOD: ALC failure

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Ick:
Late reply to this thread as I spent quite some time reparing a similar  (bult older, SMIQ02 - without the B) unit.


--- Quote from: techneut on January 22, 2021, 03:27:57 pm ---Any luck with the "IQCON no convergence" error? I have SMIQ 02E with the same error and also the same switch. Unfortunatly is the board different from the SMIQ-03B so I can't use those schematics and testpoints.

--- End quote ---

Please mind that the calibration error message (1) "IQCON no convergence" is very different from (2) "maximal level oot" and the detailed asociated debug info "IQMOD fail at frequency.."

(1)The former points at an issue of the IQConverter board: The unit is unable to set/tune or measure the RF level during Level Preset calibration. This points to an error anywhere on the HF path between LO Driver (just before the mixer) and ALC detector near the output of this board. So everything that is bypassed in CW mode (in case CW mode works without errors). Level Preset on the IQConverter is only used in Vector mode (so heterodyne path over mixer is active).
Issue sits with either of the overall ALC control loop (e.g. detector diodes or OpAmps - albeit not very probable if this is the only error, because the same components are also used for CW ALC), PIN diode errors switching the HF path, the Level Preset DAC U5 (DAC08) in combination with N1 OpAmp prducing the bias voltage, the respective current source circuitry V11, V18-V24 +V8/9 current mirror, asociated biasing or the three filters paths (750-1800;1800-2500; 2500-3300) (containing the preset PIN diodes in later board releases). In these filter paths there are MMICs that also can go bad.

(2)The latter - which is described here by zmetzing - points at the IQModulator board: e.g. here with the error on the S2 HF switch, preventing the level preset for CW in the final amplifyer stages of the IQModulator.

@techneut: In case 7 month response time are not too late ;) - focus at the IQConverter board, not at the IQModulator board with this issue.
The IQConverter comes with two main board revisions. The schematics available over the links posted here are for the older revisions, so is the service manual. The principle remained the same and the schematic is also the same in big parts. However some important details like amplifyer stages and filters have changed with the newer revision.

Antonio Borda:
Good evening,
have you found the firmware to start your smiq, I find myself with the same situation after buying a smiq03b
Boot eorom version 1.26 hx
Cpu board var 8 rev 2
ram 2048k
WIS D 115200.8, e, 1
I restart with winflashpro 1.2.27 with 5.93 it displays error in the middle of the loading it is stopped. I see quit there are other users with the same type of failure, as you have found the solution. Thanks for your help

drhex:
So am resurrecting a dropped SMIQ03B, after putting in a new screen (still looking for the outer glass/perspex), I have the dreaded 110 Output unleveled. S2 was broken, I replaced that with a HMC270 and now have output, but the ALC still complains. @zmetzing, how did you set debug to get more information? Am I interpreting your posts correctly in that the board has to be closed up to calibrate?
Some photos of the failed switch innards:

drhex:
OK, replacing the last output FET got it to work again - bit of a bother as R&S decided to solder a little sub assembly across source and drain which needed careful wrangling. Output looking good now, what I can test with my limited resources seems to work fine. Need to find an outer screen now and this is done. Please ping me if you have one kicking about, even if yellowed or such as that would be better than none :-).

zmetzing:
Congrats! These are great units that can be had for a fraction of what they cost new.

If only I could find a 6 GHz module and a fading simulator module, and then figure out how to convince the software to use them. :-)

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