I'm trying to debug a problem with an SPDIF ground loop - The problem occurs when I plug in the SPDIF from the Out of my fireface UCX into an external SPDIF interface. I took a quick look inside the fireface and looks like both input and output SPDIF are transformer coupled, however, the coax on the output measures less than 1ohm to ground, which makes me think either the output SPDIF is not isolated in the way I expect or there is some error / solder bridge

Is it normal for the SPDIF out coax sleeve to be connected directly to ground? The 'in' coax sleeve is completely isolated. If anyone has a schematic of the SPDIF out section it would answer all my questions