There is a DB3150 FileSystem Extractor. I have tested with K850_R1CA037_FS_CENTRAL-EUROPE_RED52.fbn
And extracts perfectly.
Just drag the firmware that you want to extract into the .exe file and it will start extracting itself
You can download it fom here
http://se.srzone.ru/load/0-0-0-87-20
Enjoy!!!