Re: Uniden depth finder question/repair.
How funny - I have the same depth finder and just went through the same thing. Try setting the sensitivity dial on the back. I did that, and mine started working fine. The dial is really touchy - first I adjusted it too much, and it wasn't sensitive enough, and doubled the depths. I eventually got it right - you just need to play with it in the water, in a spot where you basically know the depth.
I removed mine from the dash at first so I could see the dial - but I didn't need to. Now that I know where it is, I can adjust the dial without removing it and it is easy to adjust.
Here is a link to the manual for your model. I just bookmarked it for myself last week.
http://www.uniden.com/pdf/QT206om.pdf