Got at least 1 s5 and possibly 2 giving me a headache.  These 2 units dropped in speed before eventually just going offline.  I brought them home for testing, one seems to run fine but the other I can't get above 600GH/s.  To get the speed up I had to downclock.  They both appear to be operating but I suspect I'll be able to narrow it down to one board.  PSU is confirmed to operate normally.  Am I just going to have to ditch malfunctioning boards?  Anything else I can do besides checking cables and PSU?