My Duo 2 works off both tuners, I am currently using Tuner A, but I use a 36v motor, and a V-Box II, so I use Diseqc 1.2, not Usals.
When you tried using Tuner A did you do a fresh installation, and setup, without using any backup, then try scanning in the channels?
I think its prob time to close this one as its going in circles , what we have established.
There is no fault with the duo.
Its now working fine , it wasnt before but you did have it set up correct ?
When you get the next problem just start a new thread ,