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Thread: Teensy 3.6 does not show up in Windows Device Manager

  1. #1
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    Teensy 3.6 does not show up in Windows Device Manager

    Hello,

    I got my black Teensy 3.6 about a month ago, and it worked pretty well, until yesterday.

    I plug my Teensy into my PC, but it didn't show up in the Device Manager.

    There's no COM port nor HID device detected.

    While holding reset button down, insert USB cable, then release reset button.

    It doesn't work.

    I presume the board is dead.

    The voltage was measured on a "3.3V" target using a multimeter.

    It is recognized as "0.07V" as shown in the figure.

    Thanks.Click image for larger version. 

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    Is there any way to fix it?

    Can I check more?

    Thanks

  2. #2
    Senior Member PaulStoffregen's Avatar
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    Quote Originally Posted by caris View Post
    Can I check more?
    Next measure VIN. Normally is should be 5 volts because of USB power.

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    Hello @PaulStoffregen

    Hearing your opinion, I checked.

    "5V" is output to the multimeter

    gnd and VIN pins.

    Click image for larger version. 

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    When the board is turned on, it gets hot without any work within 3 minutes.

  5. #5
    Senior Member+ Frank B's Avatar
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    Yes, a hot board is a clear indicator that it is dead.

  6. #6
    Senior Member PaulStoffregen's Avatar
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    Usually such a low voltage (under 0.2) on the 3.3V power means there's a metal short somewhere on the board. That's not good, but it's much better than measuring about 0.6 to 0.9 volts, which usually indicates something is damaged inside one of the chips. Many times on this forum we've seen "dead" boards measuring shorted out power on 3.3V. When it's in that higher range meaning a chip is damaged, repair is usually impossible. The good news is many times with the much lower voltage you're seeing, we've seen boards come back to life once the metal short is found and fixed.

    I'd recommend getting a magnifier and bright light so you can visually inspect the board. Maybe you'll find solder or other metal object is shorting somewhere.

  7. #7
    Senior Member+ Frank B's Avatar
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    Would be interesting.. but how does it get hot if there is a short?

  8. #8
    Senior Member PaulStoffregen's Avatar
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    When 3.3V and GND are shorted together, the LP38691 voltage regulator tries to deliver as much current as possible into the short. But it has foldback current limiting and thermal overload protection. The PTC "fuse" also increases in resistance, so it also gets hot. Together those 2 parts limit the current into the short, but it doesn't shut off like a normal fuse which permanently becomes disconnected. A sustained large current flows through the short, and those 2 parts end up with all the power dissipation of 5V times whatever the sustained current happens to be (not a precise number, somewhere between 350 to 850 mA). It gets hot as a result. But those 2 parts are designed to dissipate heat, so usually they're not damaged.

  9. #9
    Senior Member+ Frank B's Avatar
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    Quote Originally Posted by PaulStoffregen View Post
    When 3.3V and GND are shorted together, the LP38691 voltage regulator tries to deliver as much current as possible into the short. But it has foldback current limiting and thermal overload protection. The PTC "fuse" also increases in resistance, so it also gets hot. Together those 2 parts limit the current into the short, but it doesn't shut off like a normal fuse which permanently becomes disconnected. A sustained large current flows through the short, and those 2 parts end up with all the power dissipation of 5V times whatever the sustained current happens to be (not a precise number, somewhere between 350 to 850 mA). It gets hot as a result. But those 2 parts are designed to dissipate heat, so usually they're not damaged.
    OK, other parts get hot, not the main CPU.
    @caris: Which part is hot?

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    @Frank B
    The parts marked with a red circle heat up immediately after connection.
    Parts close to the USB port.

    Click image for larger version. 

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    3. I took a close-up picture, can you confirm the problem with this?
    Or do you need a closer look? I can use a usb microscope.
    I uploaded it to the cloud due to the file size limit.

    https://filebin.net/zbx5f3bs4acfz12u

  11. #11
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    This part has a questionable color.

    Hmm... Was it this color originally...?

    I'm not sure because I don't have an enlarged picture when I search.

    Click image for larger version. 

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  12. #12
    Senior Member+ Frank B's Avatar
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    Quote Originally Posted by criises View Post
    This part has a questionable color.

    Hmm... Was it this color originally...?

    I'm not sure because I don't have an enlarged picture when I search.

    Click image for larger version. 

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    Looks like you may have luck.. these are the parts Paul mentioned. The big IC does not get hot?

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    Quote Originally Posted by Frank B View Post
    Looks like you may have luck.. these are the parts Paul mentioned. The big IC does not get hot?

    Thanks for the reply!

    The blue color in the photo below is definitely getting hot.

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    I'll test the parts in the picture you marked.

    I am on a business trip, so it may take a while.

    I wish I had luck.

    I'll come back! Good day!

  14. #14
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    Quote Originally Posted by Frank B View Post
    Looks like you may have luck.. these are the parts Paul mentioned. The big IC does not get hot?
    Hello,

    I came back.

    The parts you talked about don't get hot.

    This is a slightly lukewarm temperature level.

    The blue circle mark part I'm talking about is very hot.

  15. #15
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    If you look at the circuit diagram and follow the track from the 5v+ pin on the PCB I think you will find that this is the thermal fuse.
    Something downstream of the fuse is drawing a lot of current and causing it to get hot.

  16. #16
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    Quote Originally Posted by BriComp View Post
    If you look at the circuit diagram and follow the track from the 5v+ pin on the PCB I think you will find that this is the thermal fuse.
    Something downstream of the fuse is drawing a lot of current and causing it to get hot.
    Thanks for the reply.
    Hmm... what more should I check?

  17. #17
    Senior Member+ Frank B's Avatar
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    A short. Maybe a blob of solder somewhere..

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