Thanks for the hints so far, and a happy new year all around!
I did so far:
Cleaned all modules and checked all connectors
Replaced BIOS battery etc.
I found that one module on the DIG board causes the CMU to hick up, as described above.
I started with removing all extra modules from the DIG board, now the CMU boots up quick as normal an even passes selftest, as long as it doesnt get to a "spectrum analyzer" function, here it will show me an error "dsp.cpp" "ddc_drv" or similar.
According to the service manual the DIG board hosts the following modules:
-ADC
-DDC
-TXDSP
-AUC (directly above TXDSP with the cooling mat on it, havent marked it in the image)
it is possible to have each module twice as an option, therefore the extra connectors.
The unit boots up normally only if the DDC module isnt fitted, otherwise it will take an eternity..
As said, without the DDC module everything seems fine until I start the spectrum analyzer or the unit itself tries to do so (selftest) which seems logical as the DDC module is there to preprocess the datastream it gets from the ADC.
From the service manual: (courtesy of Rohde & Schwarz)
"The sandwich DDC MODULE1 is directly plugged onto the DIGITAL
BOARD via three multipoint connectors and processes the digital data
stream of the receiver. In a special ASIC chip, the I/Q shaping, the
matching of the data rate and the respective filtering (bandwidth
shaping) of the digital data stream are produced. Then follows a DSP
(RX DSP) with further evaluation of the digital I/Q data for
measurement purposes. Besides, the digital I/Q data are passed on via
the MOTHERBOARD1 to the LINKHANDLER MODULE for evaluation."
I started to reverse engineer the module, and checked all the supply voltages which seem to be correct.
So I guess this isnt repairable at all, at least not without schematics and programmed spare parts.
What would the experts do?
Change the whole DIG assembly or is there a way to get hold of just the DDC board?
Regards