Hitachi 50ux23k-- gray circles appearing

[buybeware]

I just purchased this Hitachi 50 inch rear projection 50ux23k- used--- from a friend. Now that I have it home- when I'm viewing it, I'm seeing dark/shadow circles on the screen... it's more visable when I'm watching a hockey game (or something with a lighter background).

The circle starts in the middle--- then another circle around that...etc... it extends to the ends of the screen... each circle is about 1 inch thick.

What does this mean?
Can I open up the back and clean out the dust?

Any suggestions would be helpful.

[cory]

marks caused by either defective freznel screen or dirt or dust between freznel and lenticular screens.

[buybeward]

Is this something I can clean myself? How?
Thanks!

[minnie]

Remove the speaker grill and take out the screws and disconnect the wires to remove the screen assembly.