CMU200 repair attempt - shipping damage (oh those post monkeys...)

[Yansi]

I guess the IQ interfaces are really hiding somewhere in between the 13 unused connectors on the B17 module.

If there are really two IQ mods and two demods, there must be 8 unused connectors on the B17 dedicated to these.

If I would just have a piece of a pigtail cable with MMCX on the end, would be quite easy to probe the B17 module to find what all the connectors do.  But, I have to somehow fix the damn backlight, its starting to piss me off. 

[Yansi]

Wait a minute... 

There is already a dedicated 15pin dsub on the rear panel. All signals therefore must travel through the backplane. Wondering, what the bandwidth of the baseband is.

//EDIT: The pinout of that conenctor is yummy. (not)

//EDIT2: Tried to look up in the manuals, what the IF frequencies are: Seems 10.7 MHz for RX and 13.85 for TX. See "Option R&S CMU-B17 IQ AND IF INTERFACE Technical Information" http://www.usedsite.co.kr/pds/file/CMU_Rev10_e.pdf, Annex 4: Specification on page TI.12
Baseband BW is 2.5 MHz.

[Yansi]

Okay, B17 solved so far. On to some next steps:

Repair the damn intermittent LCD backlight.

Why the rear "MONITOR" VGA output connector does not work? On either of the two CMUs I have, the monitor output provides no signal. Or so does a connected monitor tell me. And I know my monitor is good and has working VGA input. Even tried a different monitor on there, still "no signal". Needs to investigate, as having a big external screen is a big plus.

Has any of you sucessfully used the rear MONITOR output on the CMU?

//EDIT: Faulty VGA cable. F!!!!!!ck. Now I have obliterated the offending cable, so it can no more.

[Yansi]

Continuing the story:

CMU-B17: I almost thought all is well, until I found it ain't. There is a problem in the TX PATH, I get really shite output whenever I enable the main TX generator.  Noisefloor goes significantly up and the TX level is incorrect, very much lower. (Whats even more weird, is switching on FM modulation, it starts to work OK.  )

To be able to troubleshoot any further, I have tried to investigate, what is what port on some of the cards.

First, I have updated my "whats in the B17" picture with what some of the ports do, while showing how the default "bypass all" path looks like. What rest of the used ports do should be obvious from the manual Option R&S CMU-B17 IQ AND IF INTERFACE Technical Information

Then, the analysis began, just with closed modules as they are plugged in the unit. I don't want to open them and risk damaging something. But it would certainly help reverse engineering the CMU.

RXTX board:
X39 is the IF3 RX output (10.7 MHz)
X38 is yet another IF3 RX output, but few dB less signal there (10.7 MHz).
X37 is the IF3 TX input (13.85 MHz)
X36 is the transmitter's IF2 output (487.5 MHz, see it there, very low but constant level about -60 dBm)
X35 is the receiver's IF2 output (487.5 MHz, see random stuff as the analyzer is sweeping and LO2 leakage)

The digital card A7:
X701 reference input 78.000 MHz (funny, even when unplugged, everything is working like nothing happened )
X702 reference input 80.000 MHz (when unplugged, analyzer stops working. Plug back and it continues)
X703 reference input 110.800 MHz (Beware, when unplugged, firmware crashes and locks up  )
X704 something something to B41 audio analyzer or the big B66/68/76/78 card. What may it be?
X705 reference output REF2 (BNC on the back, configurable frequency, +6 dBm. Quite surprised this ain't function of the REF board.)
X706 is a receive input CH1 (10.7 MHz)
X707 is not populated, but very likely receive input CH2
X708 is a transmit output CH1 (13.85 MHz, about -5 dBm)
X709 is populated, unused, guessing transmit CH2.  Would be nice to confirm with a CRTU unit that has two RXTX cards.

Reference board:
X102 unused, likely another ref input
X103 reference input EXT 10 MHz (BNC on the back)
X104 reference output of 10 MHz (BNC on the back)
X105 outputs 27.7 MHz (for the audio B41 option)
X106 outputs 110.800 MHz (for RXTX board and B95/96 option)
X107 outputs 110.800 MHz (unused)
X108 outputs 110.800 MHz (for digiboard A7 and B17 option)
X109 outputs 80.000 MHz (for digiboard A7)
X110 outputs 78.000 MHz (for digiboard A7)

That is what I have so far.

Still don't know, why chaining the B68 option into the TX path (loop through X924 in, X923 out) causes the TX signal from A7 to be significantly attenuated and noisefloor noticably higher. Anyone any ideas? The TX generator is unusable with the B68 in the path. (Only starts working correctly when FM mod is selected)