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Thread: LCD backlight problems

  1. #11

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    Use Eneloop D cells. You won't regret it.

  2. #12
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    The problem is they aren't regular D cells size, they don't have the nub on the top. Also they would need to be spot welded together. I'm probably going to use C cells in a custom 3d printed holder. D cells NiCD are the same 5000mah as C cell NiMH, and if they are removable I can swap them when they die, and externally charge them since I don't trust old laptop chargers especially on a different chemistry. I've heard good things about Eneloops.
    Wanted: Any old clunky 286-P1 machine that has some kind of working battery or replaceable with off the shelf parts. Preferred: 10+lbs 386 machines.

  3. #13
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    Quote Originally Posted by twistedpneumatic View Post
    Also, has anyone else posted a guide on how they did an LED mod on an old laptop/industrial display?
    It's not terribly difficult to do, it's just very time consuming because you have to completely disassemble the LCD panel to get at the CCFL tube(s) without damaging the panel. It usually takes me a few hours to rebuild a LCD screen with LED backlights.

    Get some neutral white LED tape like this:

    https://www.ebay.com/itm/332745344064

    You'll need to determine how much space you have where the CCFL was. Laptop screens are usually pretty thin, so the smaller 5mm tape may not be thin enough, requiring you to either find or make a PCB with SMD LEDs that's thin enough to fit. I find that 5MM tape works in most cases. The larger 8mm tape usually works in older square desktop LCD monitors, just make sure you don't use the waterproof variety. If in doubt, take the panel apart first to get measurements.

    You also need to make sure you get the more densely packed LED tape with 600 LEDs/m vs the 300 to give both a more uniform brightness and prevent bright spots on the screen. Another good idea is to find the tape with the largest LEDs installed, like 5050, which are 5mm square. Tape that has pencil thin LEDs doesn't look as good, but you may not have a choice due to size constraints. 5mm tape usually has 2835 LEDs, which work well enough.

    In any case, the rolls of LED tape are cheap enough, you can get multiples to experiment with.

    And a high voltage buck converter like this:

    https://www.ebay.com/itm/263372679565

    A high voltage buck converter is important because power sources in LCD panels tend to be 25-50v and normal buck converters can't cope with it and will burn.

    From then, it's just trial and error. You'll need to find a sufficient power source inside the screen/laptop to cascade the buck converter off of and then set its output to 12v before you attach the LED tape.

  4. #14
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    Quote Originally Posted by GiGaBiTe View Post
    It's not terribly difficult to do, it's just very time consuming because you have to completely disassemble the LCD panel to get at the CCFL tube(s) without damaging the panel. It usually takes me a few hours to rebuild a LCD screen with LED backlights.

    Get some neutral white LED tape like this:

    https://www.ebay.com/itm/332745344064

    You'll need to determine how much space you have where the CCFL was. Laptop screens are usually pretty thin, so the smaller 5mm tape may not be thin enough, requiring you to either find or make a PCB with SMD LEDs that's thin enough to fit. I find that 5MM tape works in most cases. The larger 8mm tape usually works in older square desktop LCD monitors, just make sure you don't use the waterproof variety. If in doubt, take the panel apart first to get measurements.

    You also need to make sure you get the more densely packed LED tape with 600 LEDs/m vs the 300 to give both a more uniform brightness and prevent bright spots on the screen. Another good idea is to find the tape with the largest LEDs installed, like 5050, which are 5mm square. Tape that has pencil thin LEDs doesn't look as good, but you may not have a choice due to size constraints. 5mm tape usually has 2835 LEDs, which work well enough.

    In any case, the rolls of LED tape are cheap enough, you can get multiples to experiment with.

    And a high voltage buck converter like this:

    https://www.ebay.com/itm/263372679565

    A high voltage buck converter is important because power sources in LCD panels tend to be 25-50v and normal buck converters can't cope with it and will burn.

    From then, it's just trial and error. You'll need to find a sufficient power source inside the screen/laptop to cascade the buck converter off of and then set its output to 12v before you attach the LED tape.
    I know that my STN mono 4000E has a very thin display but the Active Color 4000E has a "bulged" lid in comparison. It's not damaged but it's made considerably thicker for the color display. All the color units of the 4000E I've seen have the increased thickness. This should give hope for getting some 5mm strips in there.

    Then the question is mounting a driver(always got a 3D printer if need be) and dealing with the brightness switch.
    Wanted: Any old clunky 286-P1 machine that has some kind of working battery or replaceable with off the shelf parts. Preferred: 10+lbs 386 machines.

  5. #15
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    I was bumbling around Ebay earlier and discovered even thinner 4mm LED tape, so there's a smaller option now:

    https://www.ebay.com/itm/254031836236

    There's also electroluminescent wire, which is smaller yet, but it has its own problems. It requires high voltage, isn't as bright and has a very short lifespan of 1-3 years depending on use and how hard you drive it.

    You don't need a driver for LED tape, just a 12v power source, hence the buck converter. If you wanted to adjust the brightness, you could desolder the trimmer pot and drill a hole somewhere for it to poke through the plastic and use wires to connect it back to the buck converter. You'd have to be careful not to overdrive the LED tape, which could be accomplished by putting a fixed value resistor in series with the trimmer pot so the buck converter will never go over a certain voltage.

  6. #16
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    Quote Originally Posted by GiGaBiTe View Post
    I was bumbling around Ebay earlier and discovered even thinner 4mm LED tape, so there's a smaller option now:

    https://www.ebay.com/itm/254031836236

    There's also electroluminescent wire, which is smaller yet, but it has its own problems. It requires high voltage, isn't as bright and has a very short lifespan of 1-3 years depending on use and how hard you drive it.

    You don't need a driver for LED tape, just a 12v power source, hence the buck converter. If you wanted to adjust the brightness, you could desolder the trimmer pot and drill a hole somewhere for it to poke through the plastic and use wires to connect it back to the buck converter. You'd have to be careful not to overdrive the LED tape, which could be accomplished by putting a fixed value resistor in series with the trimmer pot so the buck converter will never go over a certain voltage.

    Here's the problem. It's not a trimmer pot. IT IS JUST A SWITCH. You get dark and bright. That's it. I'd need to convert that into full and mid brightness.
    Wanted: Any old clunky 286-P1 machine that has some kind of working battery or replaceable with off the shelf parts. Preferred: 10+lbs 386 machines.

  7. #17
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    Ok, I opened up the LCD to see what I'm working with. TI made this very easy for me, they put the switch on its own screwed on daughter board so I don't need to worry about that. Its just a generic 8.4" active matrix panel. This is what it looks like:ijJ6pBy.jpg

    EDIT: I misread what you meant by desolder the trimmer pot. There is actually a small access door that can be flipped up using a penny on the top side of the machine. I could probably put it on there.
    Last edited by twistedpneumatic; May 10th, 2019 at 05:56 PM.
    Wanted: Any old clunky 286-P1 machine that has some kind of working battery or replaceable with off the shelf parts. Preferred: 10+lbs 386 machines.

  8. #18
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    UPDATE: I jumped the CCFL with another inverter as I suspected the bulb was fine...it was. The bulb is bright and in perfect shape when driven by a working inverter. Knowing this I might see if I can find a replacement online by searching the model number on the inverter.BmdP84T.jpg
    Wanted: Any old clunky 286-P1 machine that has some kind of working battery or replaceable with off the shelf parts. Preferred: 10+lbs 386 machines.

  9. #19
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    The inverter looks really simple, try checking some of the passive components like capacitors and resistors to see if they're bad.

  10. #20
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    Quote Originally Posted by GiGaBiTe View Post
    The inverter looks really simple, try checking some of the passive components like capacitors and resistors to see if they're bad.
    Replaced a capacitor, inverter fired right up! Thanks guys.IMG_20190512_153532.jpg
    Wanted: Any old clunky 286-P1 machine that has some kind of working battery or replaceable with off the shelf parts. Preferred: 10+lbs 386 machines.

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