Nintendo DSi's Screen Goes With Funny Colors

hello, almost 2 months ago I adapt a cellphone battery to my Nintendo DSi, works really well and didn’t give me any problems, but suddenly 2 days ago I got the 2 screens going on acid both, they were negative colors, then gray, CRAZY, I knew it wasn’t the flex cable, bc when I move it around it dosen’t goes back to normal, then I figure that in the back where the battery goes there are two little screws that adjust the screen? IDK man, but when I turn them right everything went to normal, but then a couple of minutes later, the went on acid again and I ended up disassemble the whole thing, then I clean the flex cable that goes to the R and L bottoms and it worked, but now my question is, what kind of relation has those little screws in the back where L bottom is with the screens?