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Thread: LCD Backlight Upgrade

  1. #951
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    this is the lcd unpowered to give an idea of how much diffusion is necissary at this point... if I fill the gaps with lights the light would be more even..... at 20 watts it's bright.... at 36 watts it should be better......

    these things do get hot...... I have to shut it down after about 1/2 hr.
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  2. #952
    Maximum Bitrate gork's Avatar
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    Wow great to see the LEDs coming along! For the diffuser you might try a plastic fresnel lens. You can rough up the smooth side with sandpaper to make it translucent or put a piece of vellum paper in there if the refraction of the lens is not sufficient and or the sanding doesn't make the thing translucent enough. If it doesn't work, at least you wont be out of a bunch of money. I use a diffuser similar to this behind the marquee of my mame cabinet and it works great.

    You might also consider painting the exposed parts of the copper plate with white paint (or reflective paint or reflective tape). It wont hurt its ability to dissaspate the heat, but it will certainly help with the dark spots you are seeing. Doing this ought to help more than any diffuser, I would think.
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  3. #953
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    yeah for sure get the inside of that box white, do you have the diffusers from the original backlight to try?
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  4. #954
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    did u build a PWM circuit to tone down the LEDs? it looks plenty bright from the pic and it may help with the heat.
    also as a thought for a diffuser try home depot and get one of the flourescent light diffusers and place it behind that piece of lexan
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  5. #955
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    I'm running these off pwm power supplys... I can dim it but photo's show maxed..when it is dimmed it still has the hot spots as much as when it is all the way up....

    I want to paint the inside white... but have to wait for all of the led's to go in first... I don't think painting it white will make a huge differance in the dark spots though, because these aren't like ccfl's which project all over the place.... these are pretty much more like spotlight's....I'm sure there is some reflected light hitting the copper, but I don't think enough to make a big difference


    as far as the heat...these are supposed to get hot... when it's installed & liquid is pumped through the radiator system the heat won't be a problem... but for testing there is no liquid going through these...

    I tried the home depot floresent light diffuser but doesn't work to well.... fresnel lense might work... I have to get my hands on one.... maybe staples has it?

    I don't want to use something too opaque because that will cut down on the brightness... the original diffusers are all still in the lcd to hold it togeather... I didn't remove anything but the rear most reflective backing layer... I don't think I want to remove anything else from the lcd at this point.... don't see that helping much....

    I realy think adding more led's to fill the holes should help alot too & will make the diffusion easier

    I've got to get my hands on a bigger lcd for parts.....I have a bunch of 10.4's but they'll be to small.. a diffuser from another lcd might be a big help without cutting down on the light so much.... I might have a 15" that I can butcher for it...

  6. #956
    MySQL Error Scouse Monkey's Avatar
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    Hey, good to see you have it working.

    As for the bright spots you want to adopt the 'light curtain' technique. This is what is commonly used on direct backlit screens.

    This uses a cover over the light source to stop the direct light b ut doesnt act over the rest of the area and steal light. I would get some thin perspex and start with roughing up the area over the LEDs.

    If this doesnt work try another piece and paint some white spots or possibly bond some thicker white plastic over the LED areas.

  7. #957
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    that sounds like a good idea too... I'm going to play with this some more....

  8. #958
    Super Moderator. If my typing sucks it's probably because I'm driving.... turbocad6's Avatar
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    I played around with a few different diffusers.... best results are with a sanded fresnel lens & a white piece of paper..... no hot spots at all..... only problem is that cuts the light down dramatically.... with just the freznel & no paper it's pretty good... still detect hotspots...but not as much... & she is still very bright

    I ordered 12 more led's.... this will fill the dark spots & all should be good.... with that I think just the sanded freznel will be perfect..... then I can paint the inside all white....I might actually get this thing done.... what a pain in the ***.....

    no matter what I did with the light curtain technique it showed dark spots.....

  9. #959
    Maximum Bitrate gork's Avatar
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    I had a pretty good feeling about the fresnel lens idea. I'm glad to hear that it worked out. What kind of paper did you use? Vellum would not cut down the light as much as regular paper, but lacking that you could try tissue paper as well. Still, painting it white and using the fresnel lens would probably be enough. With that much light behind the screen, even the black pixels on the LCD are translucent, so those dark spots come from seeing the color of the copper plates for sure.
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  10. #960
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    the freznel lens worked perfect & gave an even coverage of light if I held it like 5-6" over the bulbs, but when it dropped into place of only 1 1/2" above the lamps it just kinda magnified the hotspots really.... I wonder if different brands have different cuts... if the focus was right it would be perfect, but I guess it's too close... I just sanded it opaque...

    when I get the dark spots filled I'll play with it some more & I'll get a few different papers to play with.... I'm a little concerned with the radiated heat over time discoloring the paper though... might not even need it I hope...

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