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Discussion Starter #1
I have a low end NEC projector (not even HD), and it developed a problem where there are these light spots on and around the picture. During bright scenes you can't notice them, but during dark scenes they are obvious. I figured it was dust on the lens, but it turns out that no matter how much I clean the lens, they don't go away. What is that, and is there a way to fix it?

Also, when a movie has a long dark scene, (or is just a dark movie overall), it seems like the picture keeps getting brighter, like the wall is being lit, washing out the movie. And, around the movie, there are light rectangles framing the movie, about 3 of them of different intensities going out a couple feet. During bright scenes you don't see this at all. Anything I can do about that? I feel like I need some kind of little black box attached to the lens to stop these wider light rectangles from being cast onto the wall...
 

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I had an old NEC projector that had the same problem. If it's a DLP projector then there are specs of dust (or strands) on the dmd chip, not the lens. These are on the surface of the glass which protects the dmd chip. The lens is focused on the mirrors just behind this glass, so if you de-focus you should be able to clearly see the crap that's blown onto the glass. The light hits this dust and glows.
To solve this I took the cover off the projector and used a blower brush to clean the chip (which sits right behind the lens barrel). You could use a microfibre lens cleaner if there's anything stubborn on there. I seem to recall having to remove another cover inside the projector in order to reveal the light path, but it's a few years since I did it.
I also had some light spillage which I mitigated with a piece of black card near the lens.
 

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Discussion Starter #3
Oh wow, you're right. I changed the focus to blur the picture and I was able to focus ON the dust bits behind there And it looks like the night sky with a couple dozen stars, dang. Also I realized that I can obviously tell that the dust is not on the outer lens, because the outer lens spins when you change the focus, but the light spots don't spin they stay still.

I'll look up the manual for this projector and see about taking it apart, but there is a good chance I won't go through with it. The projector currently works and just has a couple light spots. I don't want to break it or cause some other worse problem.
 

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Well, I finally took apart the projector to try to fix this. First of all I took it apart more than I needed to. I took the mainboard off and then a big cover piece inside. Then I realized that I didn't have to do any of that - all you have to do with this model after you take the outer cover off is unscrew 1 screw and take a tiny cover off to access the dmd chip. You can easily see why it would get dusty, there is a huge gap below the dmd which is open to the rest of the case (which is open to the world via vents)

I cleaned it off with a camera lens brush and a microfiber cloth while shining an LED flash light into it. There were 3 surfaces: the dmd, the lens, and some kind of inner lens which must be where the light comes from from the bulb. I easily cleaned all the visible dust off all of them and it looked good to go.

Put it back together and turned it on, and focused on the dust again, there are a lot less dust marks, but, there is what I guess to be a huge smear on the right half of the screen. Creepily, it looks like a skull, so that freaked me out. Also there is at least 1 new dust mark, which is at a different focus point than the rest of the dust and smear. Now that I know how to easily get to the dirty surfaces, I need to find out how to properly clean them...
 

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I think I may have put a few drops of some old video head cleaning fluid, which is pure alcohol, on a microfibre cloth, since it evaporates without leaving a smear. I presume any glasses cleaning fluid will do similar, but obviously only ever spray onto the cloth and not into the machine!
 

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Some film is left on the surface. I would get some alcohol and a very clean MF towel.
 
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