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Author Topic: Intersting NC-900 prism problem.... Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 08-07-2016 08:29 PM                     So I finally got around to looking at this projector this morning. Looks like a booger on the prism. What it most likely is in this case is cooked insect guts. The real pisser is that this is on the rear of the front prism. In the picture it looks like its on the front side... sadly, its not. That's how clear and passive the glass is that is used on these! There are actually five fans blowing on the light engine in this projector! This has been in over three years and already needs a cleaning. We are going to get a standby light engine to install so I can pull the front prism off this engine and attempt to clean it. It appears relatively easy to do. One side of it is for sure dowel pinned at one side, it may be at both. Until I pull it and have a closer look I won't know for sure if it's pinned at both sides. If it is then pulling that off and cleaning will be pretty easy. If there is only one dowl pin then I can use feeler gauges to get the correct clearance on the opposite side set back perfectly again. So far no word back from manufacturers or NEC distributors as to weather they clean these or not. A replacement prism is about 8k. So developing a method to clean these safely is going to be pretty necessary. Mark  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 08-08-2016 06:56 AM                     Wow. How did this get in there? - Carsten  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 08-08-2016 07:08 AM                     Absolutely no idea. I'm the first one inside of this projector. Possibly a spider included during factory assembly or something...  |  IP: Logged Marco Giustini Film God Posts: 2713 From: Reading, UK Registered: Nov 2007 posted 08-08-2016 07:25 AM                     the problem is that you're looking into a prism, the damage could look very close but it may be anywhere in the assembly!  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 08-08-2016 08:55 AM                     Hmm, from the photo it looks safe enough to assume it's on the front (or back) of that exit glas. I think you can assure that assumption by using different light angles onto the dirt. Anyway, it would be heart-breaking to dump this light engine without at least trying to recover it the way Marc suggests. - Carsten  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 08-08-2016 10:24 AM                     Well, fortunately the front prism (which I call the light inlet prism) is easily removable for cleaning. There are no other visible gaps between the three other prisms the DMD's are attached to. So those should stay clean except for the one combining face behind the inlet prism. The inlet prism is secured to the engine mount by four black allen screws. You can't see the lower pair but there is also a dowel pin to locate that end. Hence my thought on using feeler gauges to get the opposite end back in perfect alignment. This goober is definitely on the rear of the light inlet prism. There is only about a 1/16th inch gap between the two prisms. So more or less impossible to clean them in place. The larger NEC prisms are very similar in construction but the rear prisms are a bit more complex. However there is like a 1/4" gap between the light inlet prism and combining prisms on those. And it is possible to clean the dust from them if done carefully. They do not get nearly as dusty though. Converting an NC-900 to water cooling would be highly beneficial in dusty environments like I have around here.You could get rid of the compartment four fans. I'd just leave the one on top.  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 08-08-2016 12:23 PM                     Keep us updated (pictures, pictures...)! - Carsten  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 08-08-2016 12:47 PM                     I will....  |  IP: Logged Carsten Kurz Film God Posts: 4340 From: Cologne, NRW, Germany Registered: Aug 2009 posted 08-08-2016 02:23 PM                     Did the owner/operator give any time after installation when this issue occurred? Any info wether this 'suddenly' popped up, or developed gradually? As far as actually insects were involved... ;-) - Carsten  |  IP: Logged Jim Cassedy Phenomenal Film Handler Posts: 1661 From: San Francisco, CA Registered: Dec 2006 posted 08-08-2016 02:32 PM                     Great photos, Mark. [thumbsup] I had a similar issue last year with a large non-dcp DLP Christie projector that suddenly developed a strange colored dark 'blotch' near the corner of the image. Shining a very bright LED flashlight through the lens, I could see there was SOMETHING inside on either the DLP assembly or one of the prism faces, but it was impossible to tell which one. By sliding a thin piece of paper in & out of the mirror & prism assembly until I saw the 'blob' disappear, I was able to determine which surface it was on. It turns out that the projector had been moved recently so that a wall could be painted. Movimg it somehow dislodged a small piece of foam rubber gasketing that was used to seal around the outside cover. The tiny chunk of foam rubber found its' way onto one of the heat filter surfaces and melted- - creating the on-screen botch.  |  IP: Logged Mark Gulbrandsen Resident Trollmaster Posts: 16657 From: Music City Registered: Jun 99 posted 08-08-2016 02:49 PM                     That's a thought Jim.... It certainly could be a piece of debris that fell in there... Projector is just over three years old... I am just not sure that (A.) I am going to get the front prism perfectly re-aligned although I think a micrometer will work fine. And (B.) That even when I do take it apart to clean it that it's all going to come off ok and not take some of the optical coating with it. That's the main reason I am not going to mess with it till I have another light engine with me in the booth. Its not going to get any worse than it is, however they have had complaints about it so fixing it in the next 30 days is important. This is going to kind of become an experiment in partial disassembly and cleaning of the prism so I can also be able to clean other NC-900 prisms. I am very good at cleaning this stuff having learned the proper techniques and chemicals to use when I was a tech at Canon. Mark  |  IP: Logged

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