Rear projector tv problems8/11/2023 ![]() Perfect size and shape to make some little bookcase speakers maybe. The TV also had two of these ported speaker boxes. I can’t quite put a finger on it, but the image quality definitely feels nicer than a normal mirror. First surface mirrors are nice since the glass doesn’t interfere with the light like a normal mirror, where the reflective surface is on the back of the glass. It was exceptionally clean and pretty, since it is a first surface mirror. This sits right up against the angled back of the TV. This is said giant shiny mirror from above. If you look carefully at this picture, you can see Michael, who took the TV apart with me. The Fresnel straightens out the expanding light rays from this lens into a collimated beam straight to your brain. That huge slanting back of rear projection TVs is actually a big shiny mirror that reflects the image towards the front screen and its Fresnel lens. ![]() This lens throws the image out towards the back of the tv. This is one of the final lenses of the DLP train. Lifters are easily seen as small square indentations under an overhang such as a clip protruding from a wall. Injection molds typically have a number of lifters which are moving subsections of the mold that allow you to mold undercuts, or places where the part would typically end up stuck on the mold. The plastic molds however, are typically crazy complicated. Injection molding plastic is actually an extremely similar process but with plastic instead of metal. You can’t see it in the photo, but there is also a little flash, or extra material, from where the two halves of the mold join imperfectly. You can also see the draft on this area of the part, further reinforcing the part line location. These marks come from the pins used to shove the hot metal part out of the mold. Here is the real dead give-away on die casting though, the witness marks. This one is pretty obvious, the parting line runs around the bottom edge of the part and up along the semicircle in the center. This is a good indication of where the halves of the mold were. You can also sort of see the draft on all the fins on the top. The surface finish and coloring of this part is pretty typical of a die-cast part with its sort of mottled exterior. I liked this part because it’s a nice example of a die-cast part. Again just my thoughts here, but that is likely because the other colors combined will make white light, so the additional ultra white is only a supplement. The clear band is smaller than the others and only occurs once. I’m guessing that this allows the projector to put out a nice bright white color if it ever needs it. In projection as opposed to printing black is actually just the absence of light, and is instead substituted by a white or clear band. This wheel is sort of CMYK or cyan, magenta, yellow, and key (black), except the key is different. Remember how we said that the DLP chip selectively reflects light? Well the light source is white light, and the DLP mirrors can’t change the color, so you need some way to make the colors we see. The black housing on the far left is where the DLP chip lives, sitting at a 45 degree angle to the optical path, selectively reflecting light up in the photo to the next optical elements. At left there are 4 lenses to prepare the light for the DLP chip, expanding the beam so it is roughly the size of the DLP chip. The empty space at center is where the color wheel goes, which we’ll talk about next. The light is directed though a little tube of mirrors, which aren’t shown, probably to roughly collimate it. ![]() The far right is the box that the light source goes in. This is the box that holds the meat of the DLP setup and optics. One method is to selectively block light, like an overhead, while the other is DLP in which light is selectively reflected by an array of tiny micro mirrors and magic. ![]() DLP is one of the two ways to project an image. The TV was DLP which stands for Digital Light Processing from Texas Instruments. If a tiny one can burn leaves, this one will probably let you start a forest fire with a flash light. One of my friends informed me of the massive Fresnel lenses inside projection TVs just as this one appeared across from the apartment. I had a few small Fresnels from my automated Nerf turret project and quickly discovered that the 3”x2” lenses were capable of burning leaves and marking wood. Rear projection TV screens are actually a massive Fresnel lens. The original prize when grabbing this TV was the screen. Old products are a goldmine of random interesting parts, and a great opportunity to take a look at design and manufacturing. After it sat there for about a week, I decided to haul it over to my place and take it apart. Someone across the street from my apartment left out this perfectly awesome rear projection TV with a “bad bulb”. ![]()
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