One other check you could perform before dismantling is to apply pressure around the screen bezel. Squeeze the front and back of the bezel together with one hand at the edges, outside the LCD viewing area. Move around the bezel and squeeze different areas. My friend had a 1400 with this problem and the squeeze test worked. This indicated poor connections somewhere inside the screen casing, possibly between the LCD cable and the LCD board. He "fixed" it with gaffer tape.