Page 2 of 2 FirstFirst 12
Results 11 to 16 of 16

Thread: New toy, but it needs daunting amount of repair (LED screen)

  1. #11
    Join Date
    Aug 2013
    Posts
    73

    Default

    Quote Originally Posted by telmnstr View Post
    Moisture penetration of SMD LEDs is apparently a big issue. They call it the popcorn effect when they take on moisture in factory then explode during soldering process. Surprise to me.
    That's actually a problem with all kinds of components. It's why a lot of SMT parts ship in sealed bags with desiccant packs and moisture indicator cards, with instructions for baking the parts if the moisture's risen above a certain level. LEDs may be especially sensitive to moisture ingress due to the encapsulants used.

    I was thinking the same thing about how would a failed LED cause 4 others near it to light up. That didn't make sense to me, but then I thought of how a pinball machine uses diodes to solve issues with column-row driven switch and coil matrixes. I guess since a LED is one way only it causes some kind of issue when driving the neighbors?
    I was thinking about that as well, but that would require the LED to fail short rather than open circuit. It's common for semiconductors to fail short due to electrical damage, but I'm skeptical that it would be a common failure mode due to moisture getting into the LEDs themselves. That said, I'm not that familiar with the chemistry involved when it comes to the materials used in the LEDs. It also depends on the driver topology.

  2. #12
    Join Date
    Apr 2008
    Location
    DC/VA metro area
    Posts
    402

    Default

    Quote Originally Posted by aberry View Post
    That's actually a problem with all kinds of components. It's why a lot of SMT parts ship in sealed bags with desiccant packs and moisture indicator cards, with instructions for baking the parts if the moisture's risen above a certain level. LEDs may be especially sensitive to moisture ingress due to the encapsulants used.



    I was thinking about that as well, but that would require the LED to fail short rather than open circuit. It's common for semiconductors to fail short due to electrical damage, but I'm skeptical that it would be a common failure mode due to moisture getting into the LEDs themselves. That said, I'm not that familiar with the chemistry involved when it comes to the materials used in the LEDs. It also depends on the driver topology.
    Yea! I just would have (and did?) assume that they are made of plastic, and are sealed against moisture to a good degree with the vulnerable part being the 4 metal legs.

    They use a column/row scanning setup. They don't use LEDs that have drivers built into them where data is shifted in (Ws2811 type things), they use driver ICs to drive columns and rows and scan through. All of the LEDs are simple R, G, B, Common pins.

    A friend is going to come over this weekend and help unstack the mildewy cases and hopefully air out / test some of the other panels (if the weather holds out) so I should be able to get an idea of how bad off the others are. Like 6-7 were marked bad with masking tape, I am a bit anxious to find out what that is about.
    Modern and Retro laser show hobbyist
    Pangolin QM16, QM32, Beyond Advanced, LSX, ADAT
    LS Pluto II x 2, custom build x 1
    http://lasershowwiki.757.org for my all encompassing laser show wiki.

  3. #13
    Join Date
    Apr 2010
    Location
    Grand Rapids, Mi
    Posts
    2,530

    Default

    Just have it done by SELEM j/k
    leading in trailing technology

  4. #14
    Join Date
    Apr 2008
    Location
    DC/VA metro area
    Posts
    402

    Default

    Quote Originally Posted by polishedball View Post
    Just have it done by SELEM j/k
    I wish! Going to inspect the rest of the panels this weekend I hope. Try to get an idea how bad the 7 marked bad are.
    Modern and Retro laser show hobbyist
    Pangolin QM16, QM32, Beyond Advanced, LSX, ADAT
    LS Pluto II x 2, custom build x 1
    http://lasershowwiki.757.org for my all encompassing laser show wiki.

  5. #15
    Join Date
    Nov 2008
    Location
    Cleveland Ohio
    Posts
    2,521

    Default

    Quote Originally Posted by telmnstr View Post
    I wish! Going to inspect the rest of the panels this weekend I hope. Try to get an idea how bad the 7 marked bad are.
    you have one more issue. I have no idea how you plan to bin the leds to match. Leds are not all the same even if the specs says so. You will have differences in wavelength and brightness so best make sure you get the right bin leds.

  6. #16
    Join Date
    Apr 2010
    Location
    Grand Rapids, Mi
    Posts
    2,530

    Default

    Quote Originally Posted by telmnstr View Post
    I wish! Going to inspect the rest of the panels this weekend I hope. Try to get an idea how bad the 7 marked bad are.

    It was pretty impressive last night. The pro-rig was tops.
    leading in trailing technology

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •