I just picked up a free LG RU52SZ51D that seems to work well except for dark vertical portions on the left and right sides of the screen (picture attached). The owners said that it had happened before, and the tech had done a mirror calibration to fix it. Sounded like something I could do, but my googling has turned up nothing for a service manual or how to do it. Does anyone have any tips, instructions, or directions on where to look? Thanks for any help.