I'm pretty sure your 3800 is like my 3200, with the TV mounted above & to the left of the main entry door. If so, there is no arm... it is a fixed mount.
The TV has 4 "buttons" attached to the rear, which fit into a multi-position rack that is firmly built into the rig. To remove the TV you first remove the speaker (pop the 2 screw covers off, the molding, then remove the screws), and then lift the TV up & out.
I replaced my TV with a larger one that I mounted on an articulated arm. I bolted the arm into the fixed mount, and went from there.
Check out this thread, and let me know if the photos are showing up:
http://www.dutchmenowners.org/forums...tage-1809.html