• Deconstructing a display

    From whit3rd@21:1/5 to All on Mon May 16 21:08:16 2022
    An old video display developed a leak (weird colors, looks like a pinpoint percussion damage), and got retired. The stand unbolts from
    the back, and that 100mm hole pattern makes it compatible with
    others, but the rest of the monitor... just parts.

    It started life as a Viewsonic VL1918 flat panel monitor,
    fluorescent backlit.

    Screws come out, get sorted into jars; steel frame bits go
    to the recycler; plastic shell parts go to landfill. The two main circuit boards handle power and backlight, and when the display frame is
    unsnapped, there's a circular polarizer film on back surface (clear
    plastic) and another on the front surface (pebble-textured plastic)
    that just peel off. The backlight is useful with the display glass removed, as a light box to view slides and negatives, but also as a target to
    someday cross-reference my various light meters' calibrations.

    What's fascinating, is the flexible Kapton cemented to the
    glass sandwich panel; there's eight drive chips mounted to Kapton horizontally, and four vertically, for what is nominally a
    1440 x 900 display; that means a couple of hundred driven
    lines per driver (and it looks like more than that
    in the printed wiring). Those chips are 1.1 x 15mm, unlabeled
    chip-on-board bare silicon. The wires, coming off both long sides,
    are too tight spaced to count (and very thin, of couse).

    It looks like about 400 lines. Just for curiosity, who makes those
    chips? What are they called, 'display drivers'?

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  • From Adrian Caspersz@21:1/5 to All on Tue May 17 06:16:31 2022
    On 17/05/2022 05:08, whit3rd wrote:

    What's fascinating, is the flexible Kapton cemented to the
    glass sandwich panel; there's eight drive chips mounted to Kapton horizontally, and four vertically, for what is nominally a
    1440 x 900 display; that means a couple of hundred driven
    lines per driver (and it looks like more than that
    in the printed wiring). Those chips are 1.1 x 15mm, unlabeled chip-on-board bare silicon. The wires, coming off both long sides,
    are too tight spaced to count (and very thin, of couse).

    COF - 'Chip-on-Film' / 'Chip-on-Flex'

    It looks like about 400 lines. Just for curiosity, who makes those
    chips? What are they called, 'display drivers'?

    Sharp?

    http://global.sharp/corporate/info/rd/tj3/pdf/12.pdf

    --
    Adrian C

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  • From whit3rd@21:1/5 to Adrian Caspersz on Tue May 17 13:44:31 2022
    On Monday, May 16, 2022 at 10:16:39 PM UTC-7, Adrian Caspersz wrote:
    On 17/05/2022 05:08, whit3rd wrote:

    What's fascinating, is the flexible Kapton cemented to the
    glass sandwich panel; there's eight drive chips mounted to Kapton horizontally, and ...

    COF - 'Chip-on-Film' / 'Chip-on-Flex'
    It looks like about 400 lines. Just for curiosity, who makes those
    chips? What are they called, 'display drivers'?
    Sharp?

    http://global.sharp/corporate/info/rd/tj3/pdf/12.pdf

    Aha! So, the assembly and fusing of the COF is why all those drivers are on separate bands, they were fabricated as transverse fusions onto a reel of
    tape; each band is a snipped-out segment of the reel. That paper does
    a good treatment of the material challenges, too. The surround goo has to
    be a special mix, to bond it for good stress relief through subsequent attachments
    and flexure. I presume the width of the tape is limited by thermal matching of the flex to both hard-PCB and the glass LCD panel.

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  • From three_jeeps@21:1/5 to All on Tue May 17 17:14:31 2022
    On Tuesday, May 17, 2022 at 4:44:35 PM UTC-4, whit3rd wrote:
    On Monday, May 16, 2022 at 10:16:39 PM UTC-7, Adrian Caspersz wrote:
    On 17/05/2022 05:08, whit3rd wrote:

    What's fascinating, is the flexible Kapton cemented to the
    glass sandwich panel; there's eight drive chips mounted to Kapton horizontally, and ...
    COF - 'Chip-on-Film' / 'Chip-on-Flex'
    It looks like about 400 lines. Just for curiosity, who makes those chips? What are they called, 'display drivers'?
    Sharp?

    http://global.sharp/corporate/info/rd/tj3/pdf/12.pdf
    Aha! So, the assembly and fusing of the COF is why all those drivers are on separate bands, they were fabricated as transverse fusions onto a reel of tape; each band is a snipped-out segment of the reel. That paper does
    a good treatment of the material challenges, too. The surround goo has to
    be a special mix, to bond it for good stress relief through subsequent attachments
    and flexure. I presume the width of the tape is limited by thermal matching of
    the flex to both hard-PCB and the glass LCD panel.
    Interesting. I don't know who makes the 'driver chips' but the bonding mechanism from the PCB to the LCD panel sounds like the thing that seems to be failing on my Samsung 50" LCD TV. When the TV is 'cold' the RHS of the picture is distorted. When
    the TV warms up, the RHS 'synchs' with the LHS and the picture becomes normal. What is this bonding agent anyway? Yes, the bonding goo it seems would have to be thermally matched to accommodate the expansion/contraction.
    One fix portrayed in some you-tube vids about the TV is to put crush-resistant pads over the strip so that when the TV is assembled, the pressure from the TV case secures the connection.
    J

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