I just had a very similar failure of my TruTrak roll servo. Coming out of sun n fun, I engaged the AP, but noticed the plane was not flying the selected course. The roll servo would engage, but would not execute the commanded turns. It would basically lock in what ever position it was in when engaged.
On the ground, I tested it and when I would input a roll command, by the heading bug, it would chatter like it was trying to turn, but nothing changed with the ailerons.
I then put in place of the pitch servo with the same results, until it just all of a sudden started acting normal again. I sent it into TruTrak along with the control head and everything looked normal on their end. I reinstalled it in the wing after getting it back and had been working well since.
