Electronics > Repair
CMU200 Rx level issue / failed loop test
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_Wim_:

--- Quote from: Michael-VK2BEA on January 19, 2022, 09:27:58 pm ---I didn't notice before but your layout is different than my RXTX board. In mine the 936 MHz filter is at the edge of the board.

--- End quote ---

Ach indeed, you board does look quite different. Something to watch out for when attempting this repair. It was already very tight on this layout, but luckaly it just fitted.
_Wim_:
Now that I look at the pictures again, I did also install the filter in reverse (output used as input). I presume these filters are fairly symmetrical, but should maybe check if no additional spurs are seen by doing it this way....
Michael-VK2BEA:

--- Quote from: _Wim_ on January 19, 2022, 09:48:21 pm ---Now that I look at the pictures again, I did also install the filter in reverse (output used as input). I presume these filters are fairly symmetrical, but should maybe check if no additional spurs are seen by doing it this way....

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I think you are right ... they should be palindromic (50 ohms in and out, passive and linear). I'll see if I can confirm on the VNA. I think there should be a way to fab an intermediate board that gives a better ground (and lifting above the other components).

BTW It seems R&S used these filters in other devices. I spotted them the other day in Shahriar's (Signal Path) repair video of the FSL spectrum analyzer. (see them here in the bottom left  https://youtu.be/60hasxvl5KU?t=1044)
_Wim_:

--- Quote from: Michael-VK2BEA on January 20, 2022, 12:42:10 am ---I think you are right ... they should be palindromic (50 ohms in and out, passive and linear). I'll see if I can confirm on the VNA.

--- End quote ---

 :-+ :-+



--- Quote from: Michael-VK2BEA on January 20, 2022, 12:42:10 am ---BTW It seems R&S used these filters in other devices. I spotted them the other day in Shahriar's (Signal Path) repair video of the FSL spectrum analyzer. (see them here in the bottom left  https://youtu.be/60hasxvl5KU?t=1044)

--- End quote ---

Good find. Probably not a "cheap" donor though...  :)
Sas:

--- Quote from: _Wim_ on January 19, 2022, 08:50:31 pm --- All tests past, even the FM Calibration that failed before!

--- End quote ---
Congratulations on the repair :-+. Can you do the 1-> 4 and 3-> 2 loop test with a positive result?


--- Quote from: Michael-VK2BEA on January 20, 2022, 12:42:10 am ---BTW It seems R&S used these filters in other devices. I spotted them the other day in Shahriar's (Signal Path) repair video of the FSL spectrum analyzer. (see them here in the bottom left  https://youtu.be/60hasxvl5KU?t=1044)

--- End quote ---
SA R&S FSH3 also has the same filters.

I don't have MMIC amplifiers yet and work stopped.
I got the same filters from the same seller. The interesting thing is, each of the filters is different, one of the filters has large offsets between the sections. The entire 3 pole BPF consists of three separate filters.

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