The schematics for different revisions of of RDDRONE-FMUK66 are available as PDF. The revision is usually printed on the PCB. Rev. C is currently the only supported revision of the FMU.
Rev. C is the latest revision of the RDDRONE-FMUK66.
Rev. B (and older) boards are not supported anymore. The schematic is left available for reference only. Please contact us if you are still using an old RDDRONE-FMUK66.