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Thread: Odd behavior with pixel bullets

  1. #1
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    Default Odd behavior with pixel bullets

    Running tests on strings ws2811 5v, I have one that when plugged in flickers wildly. I switch to another string with the same output, all is well. I disconnected all but the first 15 pixels, same issue, and when I check voltage at the end of 15, I'm only seeing around 2.72 V!!?! That's at 100 percent white. There is no clear start point where it's obvious the problem starts. Closely examining the connections and checking the solder pads inside the pixel, all looks well. So I am at a loss how to resolve this or what is the possible problem short of literally hacking off each pixel one at a time.... Any idea what could cause that much of a low reading when the source power is confirmed working? A different string of 54 measured at the end of the string on the same output gives me 4.6V

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    Default Re: Odd behavior with pixel bullets

    Quote Originally Posted by XmasinVancouver View Post
    Running tests on strings ws2811 5v, I have one that when plugged in flickers wildly. I switch to another string with the same output, all is well. I disconnected all but the first 15 pixels, same issue, and when I check voltage at the end of 15, I'm only seeing around 2.72 V!!?! That's at 100 percent white. There is no clear start point where it's obvious the problem starts. Closely examining the connections and checking the solder pads inside the pixel, all looks well. So I am at a loss how to resolve this or what is the possible problem short of literally hacking off each pixel one at a time.... Any idea what could cause that much of a low reading when the source power is confirmed working? A different string of 54 measured at the end of the string on the same output gives me 4.6V
    My first thought is to check the connector at the start of this problem string. It seems like you might not be getting good V+ to the 1st pixel. Just a thought.
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  3. #3
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    Default Re: Odd behavior with pixel bullets

    You can measure voltage in wires without cutting them. If your meter doesn’t have sharp enough tips to push through the insulation you can use a needle or push pin to pierce the insulation to get the reading.

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    Default Re: Odd behavior with pixel bullets

    Quote Originally Posted by StickyWicket View Post
    You can measure voltage in wires without cutting them. If your meter doesn’t have sharp enough tips to push through the insulation you can use a needle or push pin to pierce the insulation to get the reading.

    So basically, poke each section until I identify a drop off or change, cut it out, re-connect, re-test?

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    Default Re: Odd behavior with pixel bullets

    Quote Originally Posted by XmasinVancouver View Post
    So basically, poke each section until I identify a drop off or change, cut it out, re-connect, re-test?
    Yup, you’ll need to figure out which wire is dropping voltage.

    You should be able to figure this out by connecting one end of your meter to the negative off your PSU and the other end of your meter on the positive at the far end of the pixel string.

    Then do the same thing but use the positive off your PSU and negative off the far end of the pixels.

    One of those two should give you a lower voltage. It’s that wire you’d want to check.

    If they both measure the same voltage (low) then you’ll need to check both positive and negative at each test point.

    The fastest way to find the bad pixel/connection is to use binary division which is just a fancy way of measuring in the middle of the pixel string and then measure the middle of the section to the left or right of your last measurement point until you find the voltage drop point.

    So with your 15 pixel string measure between 7&8, if the voltage is correct then the problem is to the right of that point, so you’ll next measure between 11&12.

    If the first measurement was incorrect then the problem would be to the left of that point so you’d next measure between 3&4 (or 4&5)

    This might be a bit over kill on 15 pixel string but using this same logic on any larger string will lesson the amount of test points until you find your problem.

  6. #6
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    Default Re: Odd behavior with pixel bullets

    Quote Originally Posted by StickyWicket View Post
    Yup, you’ll need to figure out which wire is dropping voltage.

    You should be able to figure this out by connecting one end of your meter to the negative off your PSU and the other end of your meter on the positive at the far end of the pixel string.

    Then do the same thing but use the positive off your PSU and negative off the far end of the pixels.

    One of those two should give you a lower voltage. It’s that wire you’d want to check.

    If they both measure the same voltage (low) then you’ll need to check both positive and negative at each test point.

    The fastest way to find the bad pixel/connection is to use binary division which is just a fancy way of measuring in the middle of the pixel string and then measure the middle of the section to the left or right of your last measurement point until you find the voltage drop point.

    So with your 15 pixel string measure between 7&8, if the voltage is correct then the problem is to the right of that point, so you’ll next measure between 11&12.

    If the first measurement was incorrect then the problem would be to the left of that point so you’d next measure between 3&4 (or 4&5)

    This might be a bit over kill on 15 pixel string but using this same logic on any larger string will lesson the amount of test points until you find your problem.

    You would think I would already have experience with this going into my 4th season (3rd with pixels), but I've been incredibly lucky to NOT have any dead pixels like this issue. It was weird, because at first, it looked like every one of the pixels was affected the same, no sudden point of change. It was normally a 50 pixel string, but I narrowed it down to the 15 at the start since it happened even with it disconnected (string was 15 pixels +35 pixels via jst). Luckily, I can report this resolved. The techniques above are perfect (except for the part realizing my multimeter leads were NOT sharp enough to pierce the wire easily....but they WERE sharp enough to pierce my hand! lol). I turned it up to 100 percent white again, and this time, I noticed a sudden but slight detectable change between two pixels. Cut out the one that was at the start of that section, and boom, stable light! Thanks everyone. Having said this, if anyone is newer to this whole thing, and comes across this post, do NOT start chopping off pixels for guess work. Use the methods suggested by the other posters to begin with, and only cut out when you have some kind of indication or evidence it's likely the cause
    Last edited by XmasinVancouver; 10-02-2019 at 01:55 PM. Reason: clairty and added info/warning

  7. #7
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    Default Re: Odd behavior with pixel bullets

    I had 3 bad pixels in my 2000 light megatree on my first year with brand new strings. Same thing, 100% white showed several symptoms. 1: flickering pixel 2: single color pixel 3: random "tearing" of colors past 1 pixel.
    Replaced all 3, no problems.

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