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Thread: USB device to USB port Conundrum.

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    Default USB device to USB port Conundrum.

    As per the title I have a USB device to USB port Conundrum.

    I have 2 vehicles with twin USB ports with battery voltage display onboard. Both types are fitted to ignition switched fused circuit. USB ports are different brands.

    I have 2 Garmin Glo GPS units. Look identical, one is a year older than the other.

    All worked well until recently. Garmin Glo #1 stopped turning on with vehicle #1 & voltage display of the USB flashes 888 in port A, in port B voltage reads normal battery voltage but device does not switch on with ignition on, other device - dash cam, plugged in turns on fine with ignition on either port A or B. Removing dash cam does not help.

    Tried Garmin Glo #2 in Vehicle 1, works perfectly as expected in either USB port, no issues, including with dash cam plugged in.
    Tried switching USB cables & batteries between Garmin Glo #1 & #2, no change.

    So I move to Vehicle 2, both Garmin Glo #1 & #2 work perfectly with either cable or battery installed in different combinations.

    So my solution is to swap the Garmin Glo's between vehicles. Just delete pairing & pair new combination.
    Problem solved?
    Well it is, however I don't understand for sure why Garmin Glo #1 has divorced vehicle 1?
    Is it maybe a USB output voltage handshake issue?

    Would really like to know why.
    Last edited by Tiny; 30-09-22 at 07:12 PM.
    Cheers, Tiny
    "You can lead a person to knowledge, but you can't make them think? If you're not part of the solution, you're part of the problem.
    The information is out there; you just have to let it in."



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    Ok, so I sorted it out. I now know why this happened.

    2 reasons connected together.

    Reason 1: the Garmin Glo#1 has a battery connection issue, the device however works without the battery even installed when plugged into a USB port that has 5v output only. Such as vehicle #2.

    Reason 2 : Vehicle #1 has a USB output that is multi-voltage auto selected when device is plugged in, so works ok when the Garmin Glo device has a solid battery connection that causes the device & USB port to work at the correct voltage. When the battery connection is lost, the device & USB port can't decide on a voltage, so the port shuts down.

    The device I used to monitor what was happening is this handy little USB testing tool.



    Hope this helps someone who encounters a similar issue.
    Cheers, Tiny
    "You can lead a person to knowledge, but you can't make them think? If you're not part of the solution, you're part of the problem.
    The information is out there; you just have to let it in."

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