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12V DC adapter - Have I blown my kit!??

Discussion in 'Electronic Basics' started by [email protected], Mar 2, 2006.

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  1. Guest

    Guys, please help me....

    I have a piece of audio equipment (Firewire audio interface) that
    requires 12V DC (1000mA)
    I bought it in the states with a US adapter and step down convertor
    (240->110). Everything was working fine until I thought I should go out
    and buy a UK voltage adapter to replace the cumbersome setup of AC
    adapter -> step down transformer -> US/UK plug.

    I bought a '1000mA Variable Voltage AC/AC Adapter' with a 12V setting.
    After plugging it in, the lights came on and then went out on the
    device, andthen nothing! Is it because I bought an AC/AC adapter and
    not AC/DC adapter?? Could this cause the kit to stop working?? Its
    gonna be such a pain to try and return this to the store I bought it
    from in the US (Im in London), any help would be seriously appreciated.

  2. Guest

  3. John Fields

    John Fields Guest

    Not only could it, I'm afraid that's what did it.
    The bad news is that 12VAC is really 12VRMS, which comes out to a
    voltage out of the adapter which alternates between 17 volt positive
    and 17 volt negative peaks.

    There is no good news, (unless the thing has reverse polarity
    protection and all you've done was blow a fuse), and on top of it
    all you've blown the warranty as well.
  4. John Fields

    John Fields Guest

  5. Greg Neill

    Greg Neill Guest

    Interesting. The spec says "Powered via DC supply or FireWire bus",
    but the Closeup View of the rear of the unit shows a power connection
    labelled for a 9V AC 1000mA supply.
  6. Guest

    Thanks John. That was an excellent reply. Very helpful. I know Ive got
    no chance of getting it repaired under warranty, but it would be great
    if I could get it repaired instead of paying another $400 for a new
    one!! What do ya think?
  7. John Fields

    John Fields Guest

  8. Tom Biasi

    Tom Biasi Guest

    Maybe the unit has reverse polarity protection. Since you supplied it with
    AC instead of DC the polarity was reversed for 1/2 cycle. Open the unit and
    look for a fuse near the input.
    Also, Did you try the unit again with your original setup? You may have
    cooked the adaptor instead of your unit. ( If you are lucky)
  9. Guest

    Jeez, Im astounded by how helful you guys have been. John, thanks for
    the link I will contact them tomorrow.

    Tom, yes, I have tried the original adapter but it doesnt work. And
    there is no way I am going to open this unit up, Im just not confident
    to do so!!

    Thanks guys, you really have helped me. cheers.
  10. Phil Allison

    Phil Allison Guest

    "Greg Neill"

    ** True - but the pic in the User Guide ( pdf file ) shows the same
    co-axial socket labelled " 12V DC 1000mA "

    No polarity markings are shown - very bad.

    ........ Phil
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