Summary of steps / instructions:
1) Remove the Focus and Zoom rings.
2) Remove the front grill.
3) Remove the lens assembly.
4) Use compressed air to blow out the speck of dusts causing the dust blobs to appear on the screen. (Please be VERY careful of condensation, dripping, and impurities from canned compressed air.)
5) Reassemble everything.
The first 2 pictures show the "before" shot with the dust blobs. The last picture shows the screen after cleaning. The projector is only 8" from screen when I took these pictures (that is why they are out of focus, but the blobs are much easier to see). You can also project onto a piece of paper about 8" away.
I used the tweezers to lasso the string around the focus and zoom rings. Also, a *magnetic* screwdriver is highly recommended. Note: I already have the rings removed in the below picture.
The small CO2 spray is cleaner, but weak. The can spray is powerful, but may contain impurities. Follow JeffBK's suggestion to test the spray on a mirror first (see post 19 below).
I came up with the idea to lasso the rings with a string and pull, rather than prying it with a screwdriver and risk scuff marks.
There are 3 locking tabs per ring. Use the lasso to pull one *tab* at a time
. Do not attempt to pull the entire ring at once. It would be too tightly held. I borrowed D-Train's idea to mark the position of the rings with tape before disassembly.
Below, you can see the 3 tabs holding each of the rings.