I have a Proxima dp-5900 that i purchased second hand. The problem lies in that there is a box that is projected in every image that is all yellow. it is a perfectly square edged box that lies on top of any and every image. I have had the projector apart down to bare bones, cleaned every mirror, and made sure the was nothing unusual blocking the path of light or anything. Besides this strange yellow box, everything works great! Any ideas on what this is or how to rid it of this nuisance?