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Thursday, July 2, 2015

Teardown of old NEC MultiSync MT Projector

        A few months ago I got my hands on an old NEC Projector from the local flea market for almost nothing (20 Euros or so).
Of course, after carrying up the stairs to my apartment, which is no mean feat, because this thing weighs about 30 kilos, I followed the normal procedure for such a nice piece of old "vintage" electronic gear, which was to stand back and admire it. Ain't she a beaty?

 After getting my trusty screwdriver set out, first I wanted to see the lamp in this thing. Pretty ordinary for it's day, but what really surprised me was that it probably had been recently replaced - or so it said in the menu. Only 600 hours of run-time? What a score.

So why take apart a perfectly functional projector? Well, for one, the 640x480 maximum resolution this thing has isn't really of much use....for anything. Another reason is that it has lots of nice components which are worth much more than what I pain for it. But the main reason is curiosity. I just want to rip it open then drool over it while I try and figure out what everything does.

So,  first thing, the lamp. Looks nice an beefy, and really nice thing that the High Voltage power supply for this works independently of the projector's "mother board". Of course I couldn't resist not playing with it.

Top notch job on this. Looks like the engineers that worked on this design did a really nice job. I mean, it did cost about 10.000 dollars new....back in the 90's.
In fact, this entire thing was really nicely engineered and  with quality parts. Rubycon and Nichicon caps, Omron relays, really nice BNCs and connectors on the front. And also, a ton of quality optics in it.

                                                   (FYI:That's in centimeters, not inches)

After making my way through the jungle of wires inside this thing, I finally got to the main power board. As I said, really nice design. No cheap Wan-Hung-Lo brand caps here, thank you very much.
Input filter, MOVs, this thing's got it all.
The board is mainly dedicated to the switch-mope supply, but there's also a smaller transformer, probably powering the analog part of the main logic board i.e the op-amps for the video output.
Also, notice the amount of EMI suppression this board has on it (especially the analog section), and also  the forest of electrolytics scattered all over.

It took me the better part of a day to get to the metal chassis for the optics  of the projector. Everything was either  tied down with cable ties  or screwed to something. Like I said...quality.
But once I got to the optics....

I spent another day carefully getting every mirror out and the trying to figure out how this thing actually produced an image.
And this is what I came up with:

Excuse the hand drawn schematic, but I really suck when it comes to expressing my inner artist.
Basically, the light from the lamp is split into three optical pathways, each corresponding to the colors  Cyan, Magenta and Yellow. This is done with two dichroic mirrors. For those that don't know what a dichroic mirror is (don't worry, I didn't  know either before this teardown), it's a mirror that only reflects a certain wavelength of light, while letting the rest of the spectrum to freely pass through it without much disturbance (i.e. reflections or refractions).
There are also two other "normal" mirrors that are there only to help guide the light to the  main  objective.
Now, after the colors have been separated, the image has to be produced somehow. This is where three LCD displays come in. The video data is taken from the input panel,  then the processor  splits that up into three colors, then sends each color channel data to the LCDs. The LCDs are almost transparent (they have a darkish tinge to them) so some  light is lost at this stage. Also, in front of two of the LCDs there are polarizing filters - one vertical and the other horizontal. I haven't quite figured this part out yet, I don't know how they tie up in the final image.
From here on, all that;s left to do is join the three optical path with some clever use of optics into one beam, then send it on it's way to be projected on to whatever surface  someone desires (as long as it's white).

Now, I'd like to mention that although it's much nicer for the eye to have this kind of splitting of the video data into three separate  colors, it's expensive as you need a lot of quality optics. Also there is a lot of light lost because the dichroic mirrors do not reflect 100% of the light and because the LCDs are somewhat dark, so the final image looks really dim. So a lot of light is needed to be pumped into this thing to get  a relatively ok picture on the other end.
So, that's why we're stuck with the color wheel in today's projectors that make you see stars every time you rapidly move your eyes when looking at a modern projector (or should I say the image projected by it)

If you would like to know more about the color wheel I mentioned, watch this video that Ben Krasnow made, detailing how modern projectors work. It's worth it, trust me.

For more information on this projector, you can visit:


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