So the story continues......with a happy ending, I hope.
It appears to be a cable issue now. I quit in frustration last night but with a clear head this morning I went back to the obs and changed out all the cable....now downloading and cooling.
That's really good to hear! Sometimes the best thing we can do is sleep on the problem and in the morning with a cool head it's easier.
After 20 years attending to scientific instruments (mostly a mass spec) I know well that there are times when you should walk away. Sometimes for just a minute, sometimes overnight. Only occasionally do I think it should be forever. The other thing is that no one ever complains when an apparently major problem turns out to be a cable (or $20 switch etc).