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Author Topic: Intersting NC-900 prism problem.... Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-18-2016 03:26 PM                     I have these pictures and confirmed via test patters that the odd shading is something to do with the red DMD only. I am guessing its separation of the red filter on the prism block. Air filters get changed regularly and the light engine is buried pretty far inside this projector for a glob or some grease or something to get carried that far inside. Plus the green and blue are clean as a whistle. Doesn't look like DMD failure either as no stuck or misbehaving pixels at all. So I am suspecting the actual prism in this case. I will find out this coming weekend and report back. Mark  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 07-18-2016 06:22 PM                     wait a second... are you suggesting that an NEC projector actually failed on field without notice? And the customer cannot fix the problem in 5 minutes? Are you serious?  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-18-2016 07:07 PM                     You got it! This is the forth legitimate failure out of 335 projectors some of which are going on seven years old. The other outright unannounced failures were a bad xenon ballast in an NC-1200, a blown ballast in an NC-900 and a failed lens driver board in an NC-900 because the factory did not route a motor wire correctly. Otherwise these things just keep running and running. I have had some white switch failures, not like that wasn't common knowledge though. Crappy German circuit breaker! We leave them all on now. Have external power switching arrangements. The GDC's have been even more reliable than this with only two media block failures in seven years. Yes, I feel like the Maytag man... All I generally do is updates (remotely at 334 of the sites) and on site image and sound checks twice yearly. Mark  |  IP: Logged Steve Guttag We forgot the crackers Gromit!!! Posts: 12814 From: Annapolis, MD Registered: Dec 1999 posted 07-19-2016 07:43 AM                     jeez Mark! That is a simple purity adjustment. Use the degaussing coil first then by adjusting flyback yolk, you should be able to get a pure red field. Actually, dirt getting into an NC900 is VERY VERY easy. I was amazed at the training class when we dug into one just how far dirt gets into them...it gets EVERYWHERE...we pulled the light pipe and it was EVERYWHERE.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-19-2016 09:03 AM                     LOL! That purity thing is the first thing that came to mind! I wish it was that easy! And... we have LOTS of dirt out here in many desert places. I see a little dirt in most model NEC's mainly due to those crappy cardboard filters Wrong used to sell, but this Idaho location is not so bad. The worst place is Jackson Hole, WY where they change filters every 60 days and they buy filters by the case. Its definitely NOT in the illumination system because the blue and green are perfect. Minor dust in the illuminating system isn't going to show up like this anyway. Its either a giant grease blob that's gotten just on to the red prism, or its the red filter separating from the prism itself. That prism also uses heat pipe type cooling and some of those are liquid filled. So it's also possible the red heat sink sprung a leak if that's the type they use. The theaters popper is exhausted outside... so it's not from that. Checking to see if Wrong even repairs these prisms or if they have to be bought outright. But I will go take a look at it before any decisions are made there... Mark  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 07-19-2016 03:43 PM                     Are DMD's using colour filters? I though the role of the prism was to split the colours itself!  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 07-19-2016 04:03 PM                     3DLP is definitely not using color filters, that's one of the reasons for the increased light efficiency of 3DLP technology compared to other technology that does use color filters. But the prism itself consists of multiple components which are glued together. It's quite plausible the red component is separating itself from the rest of the block, due to a slight production error. Those things are exposed to quite some heat over time and the continuous contraction and expansion might be a factor in this.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-19-2016 04:32 PM                     Yes, standard DMD - Xenon systems have to... Or you'd be overlapping three monochrome images... The prism combines the colors... Not the suspect prism but one just like it...  |  IP: Logged Marcel Birgelen Film God Posts: 3357 From: Maastricht, Limburg, Netherlands Registered: Feb 2012 posted 07-19-2016 04:52 PM                     quote: Mark Gulbrandsen Yes, standard DMD - Xenon systems have to... Or you'd be overlapping three monochrome images... The prism combines the colors... Please keep in mind that a prism is a splitter and multiplexer, not a filter. A filter blocks stuff, a prism splits and combines it.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-19-2016 08:55 PM                     The filters are generally on one of the passive surfaces of each DMD's prism where the light entering is first filtered and then reflected off the face of the DMD. The latter is the most common way I have seen 3-DLP done with RGB filters and some other trim filters involved. Its also an additive color system. Mark  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 07-20-2016 06:08 AM                     Mark I'm not 100% sure on DLP but are you sure the TRIM FILTERS are there to just trim the colours and make the spectrum DCI-happy - as the notch filter does. A prism splits white light into the full spectrum, I thought it was designed to split white light into R/G/B and onto the relative DMD's and then another prism would reassemble the picture. Sony are doing that differently, light is indeed filtered and split into RGB - then reassembled by a prism into a single image. I'm not sure of the above to be honest, but I've never heard of RGB filters in a DLP engine to be honest.  |  IP: Logged Kenneth Wuepper Phenomenal Film Handler Posts: 1026 From: Saginaw, MI, USA Registered: Feb 2002 posted 07-20-2016 06:45 AM                     The use of a prism was chosen for the total internal reflection of light. The direction of the image is changed inside the prism where other methods, like the front surfaced mirror, have loss and can deteriorate the image with dust, surface defects etc..  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 07-20-2016 07:54 AM                     A prism (combination) only can not separate colors as needed for a (white light source) 3chip projection system. It is always a combination of prisms AND some sort of color filter. The diffraction aspect of a prism is not used for color separation here. Usually, the prism combinations used in 3Chip projectors have color selective dichroic coatings for the color separation. Wether you consider this coating part of the prism combination or call it 'prisms + color filters', is up to you. - Carsten  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 07-20-2016 01:56 PM                     Thanks Carsten, I did not know that.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 07-20-2016 03:17 PM                     If you pull an NEC or Christie engine you can see the seperate R,G,B filters as part of each prism. The trim filters I am pretty sure are in the optical path before the engine and there may also be other trim filters or coatings to do the trimming applied to certain prism surfaces as well. There are T.I. technical papers on the web pertaining to color wheel type filters, their trim filters and such but nothing on 3-DLP. Mark  |  IP: Logged

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