I have an old grey face ADI 648 and a more recent (late 2000’s) blue face ADI-8 DS unit that each have a single flickering optical port. A few years ago, I had new power supplies installed in both units after seeing info that a failing PSU might be the issue but it did not solve the issue. About the time I received them back I upgraded my studio to M-32 and ADI-8 QS so they have been offline with no hours on the new PSU’s. I’m getting ready to bench these as well as quite a few other RME ADI units, to insure their functionality before offering them for sale. Any feedback as to what the issue might be with this flickering at an ADAT output would be appreciated.