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R&S FSIQ 3 RF converter repair

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EricG:
I have Rohde & Schwarz FSIQ 3 signal/ spectrum analyzer that's been in storage for a while while I moved. When I powered it up this weekend the "OVLD" indicator remains on even with no input connected. running the self test indicates indicates RF converter failure. The almost useless "service manual" says that this is indicative that the first mixer has failed and the whole RF converter board needs replacement. I'm not happy with the prospect of finding a replacement since R&S p/n 1065.6768.03 seems to be almost unobtanium.

However, I noticed in the system messages menu that message 10130, "Err Reading I2C EEPROm on RF_MODULE board" was displayed. which brings me to my actual questions.

1. Is it possible that the EEPROM contains settings that allow the RF converter board to function properly and that just replacing the EEPROM might bring this board back to life? provided of course that those setting could be restored through calibration or some other means. If so, has anyone attempted this?

2. is there any USEFUL service information for this instrument (detailed schematics etc). the Service Manual isn't very detailed or helpful.

3. Is there a good source of R&S spares somewhere that has eluded me? searching Ebay and other sites does not drag up very much.

Any help would be very much appreciated

EricG:
On the off chance that rohde and schwarz still had replacement parts for these I contacted their service dept. they had 2 modules in stock. a refurbished module and a new(!) one. R&S wants ~$10k for the new part and ~$2k for the refurb. Considering that working, units on ebay are running in the $2500 range, replacement parts seem a bit spendy.

one thing that I did notice when I removed the module from the chassis it that there was no cover on the front and back side of the module like there were on the other modules. this leads me to believe that the previous owner may have mucked about with the unit prior to selling it to me.

ogden:

--- Quote from: EricG on April 08, 2019, 10:10:51 pm ---However, I noticed in the system messages menu that message 10130, "Err Reading I2C EEPROm on RF_MODULE board" was displayed. which brings me to my actual questions.

--- End quote ---

In case it is not dead EEPROM but whole I2C bus failure (disconnect or lockup) - that may lead to whole lot of other problems including loss of module functions. There could be other I2C slaves such as gpio extender chip(s) that often are used to control digital step attenuators, VGA's and so on. You shall check cabling/connectors first, perhaps look at I2C bus using scope.

EricG:
I think that the I2C bus is common with all the modules, so if there was a bus failure, I would see other modules report similar errors, but as I said I'm lacking any reasonable service documentation to say anything educated.  All of the modules in the system connect to a common back plane for command/control/power, with coax jumping from module to module carrying the high frequency stuff so the number of cables to check is pretty small. I think next steps are to monitor the I2C bus to see what's actually happening as you suggest.

ogden:

--- Quote from: EricG on April 10, 2019, 10:15:25 pm ---I think that the I2C bus is common with all the modules

--- End quote ---

I think that would be worst design decision one could make while building very complex and highly modular device. Better do not assume anything, verify everything

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