Often, Antminer S2 come with an LCD screen which is very bright and difficult to read because of lack of contrast.
Here is how to adjust the contrast :
First, gently peel off the front "Antminer" label covering the screen :
Then you'll notice three tiny holes around it. The hole in lower right position contains a very small pot, which you can adjust using a precision "+" screwdriver :
And that's it ! You know have the perfect quality picture you've always dreamed of !
All you have to do then is to put back the "antminer" label you gently peeled off at the beginning : it should be still sticky enough.
You can then go back to your regular occupation.
Easy...