Film-Tech Forum ARCHIVE: NEC NC900C prism issue on the blue DMD side, likely dust contamination

This is topic NEC NC900C prism issue on the blue DMD side, likely dust contamination in forum Digital Cinema Forum at Film-Tech Forum ARCHIVE.

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Posted by Paul Looker (Member # 5420) on 12-22-2015, 12:02 PM:

prism issue on the blue DMD side, likely dust contamination. That's what NEC support said anyway. I just wanted to hop on here for a second opinion and to see if anyone could tell me if this was something I could take care of myself instead of having a costly service call. Here are the blue and white test patterns where it is visible. Its really hard to see on white but there is an area of yellow discoloration in the red circle.

And here is a shot of what it looks like on screen while content is running.

That's a close up shot of the blue discoloration that shows on black picture. The test patterns are running at flat. This is at the bottom of the frame because the feature I grabbed this from is scope. The discoloration is in the same spot flat or scope though.

Any thoughts guys?

Posted by Frank Cox (Member # 6258) on 12-22-2015, 12:36 PM:

You're sure it isn't a stain on the screen itself?

Posted by Alan Gouger (Member # 543) on 12-22-2015, 12:50 PM:

The % of blue combined with a larger % of Red and Green = white.
It makes sense it would be harder to see on anything but Blue background. Judging by the photos most likely some form of contamination on the Blue DMD.
The new 1201 Blue Phosphor ( revamped NC1100L laser ) has a sealed light engine. Going forward if that becomes common that should minimize the risk of contamination.
In your case this may require a service call by a qualified technician.

Posted by Paul Looker (Member # 5420) on 12-22-2015, 03:12 PM:

Definitely not a stain on the screen. Does anyone know of any technicians in the Pittsburgh area?

Posted by Mark Gulbrandsen (Member # 72) on 12-23-2015, 06:48 PM:

Also check the front lens element for a glob of stuff and the rear element if you feel comfortable pulling the lens. It's a twist lock affair. I have not had any issues with NC-900's light engines being contaminated and I've installed just over thirty of them. I have had a couple NC-2000's become contaminated due to Strongs crappy filters. It is possible for a competent technician to clean some of the prism on site. Just beware that you get a technician that's competent with optical cleaning.

Mark

Posted by Steve Guttag (Member # 268) on 12-24-2015, 03:50 AM:

I've now seen the inside of an NC900 with some hours on it. A LOT of dirt flies around in there...even with NEC's filters. It is quite easy to believe that some dirt has made it to the prism area (and/or light pipe).

Posted by Marco Giustini (Member # 4544) on 12-24-2015, 09:36 AM:

To be fair the cleanest projectors are the Christie's. It's a shame, it wouldn't take much to improve Barco's and NEC's.

Posted by Steve Guttag (Member # 268) on 12-24-2015, 10:50 AM:

It all depends on Christie. The CP2208-CP2215 isn't the cleanest projector in the world. Christie also doesn't filter their lamp compartment on any of their projectors.

Barco filters some things with a wire mesh filter that keep boulders out but not fine dirt at all. They also let the LPS fend for themselves and make the inlets on the "C" series hard to reach. They also have a fan that blows on the back of the lamphouse/Lamp Info Module ("C" series) that gets unfiltered air.

What air you start with also has a great effect on the outcome.

Posted by Marco Giustini (Member # 4544) on 12-24-2015, 12:37 PM:

the 2210/2215 should have a sealed light engine, maybe that's why filtration is reduced.

I agree with the booth air: in my cinema I'd have filtered air in the first place. As you say it would make a massive difference. It used to be a massive difference on 35mm!

Posted by Paul Looker (Member # 5420) on 12-25-2015, 08:14 PM:

Mark, I feel comfortable pulling the lens if I could get a step by step instruction for someone (me) that has a hard time reading manuals. I saw it needs to be centered. I'm not 100% on how the lens comes out but I didn't even really get that far because read and read I couldn't figure out where exactly it was telling me the control to center it was.

Posted by Marco Giustini (Member # 4544) on 12-26-2015, 05:50 AM:

I doubt that comes from behind the lens but it's indeed something to try.

Another thing you can try is this: place a piece of white paper in front of the lens, say 1-2 metres away. Now zoom the lens in either directions till you can focus the dirt on the sheet. You should be able to see that spec of dust very clearly.

Posted by Mark Gulbrandsen (Member # 72) on 12-28-2015, 10:24 PM:

Briefly, There is a lens lock lever you hold and then the lens twists about 33 degrees to pull straight out...