Hi guys.
The blue filter can degrade and the lcd in the blue line can also deteriorate.
With the top off, slide a piece of paper in between each lcd and filter. When the smudge disappears, this should indicate which light channel the fault is on. The picture will change colour as you do this. You may even be able to see this smudge on the filter, or the lcd, if it is on either.
I have had something similar on another type of projector. It turned out to be a foriegn object on one of the filter/lcd's. But, it may also be behind the filter within the engine.
If you focus the smudge as best you can, get a thin cotton bud and put it between the filter / lcd and it has the same focus, you are in the right area. Simararily, if you can get it between the lcd and prism, this might also help.
Hope this is clear???