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Dangerous PC Speakers

Discussion in 'Hobby Electronics' started by Phil Allison, Jun 28, 2003.

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  1. Phil Allison

    Phil Allison Guest

    Hi to all,

    When I upgraded my PC recently a pair of small, self powered speakers
    were included in the deal.

    These were the Lepra brand model LS699.

    After a while I noticed a burning smell coming from the area of the
    monitor but it was not that - the speaker with the PSU and amp inside was
    the culprit. On opening it I found the tiny PC mount transformer (no plug
    pack is used) was running so hot it had blackened the insulation tape on the
    primary winding and was much too hot to touch.

    The tranny would be about 2 or 2.5 VA from its size ( core 28 x 25 x
    12mm ) and powered a TDA2822M 8 pin dual amp IC - but only just. The
    primary magnetising current measured 37mA and the resistance about 3500 ohms
    when hot - that means almost 5 watts of heat loss in the primary alone - no
    wonder it was so damn hot !!

    The tranny has only *basic insulation* and no thermal fuse - the
    plastic bobbin melts like butter if you apply a soldering iron. There is
    only 0.7mm of plastic separating the windings.

    There is strangely no double insulation symbol on the unit, but there
    is an approval number ( N 10752) - for all that is worth.

    I am concerned that some trannies will burn and fail with a breakdown
    from primary to secondary and make the input plug live.

    Any one else seen this problem or another similar one ??

    .............. Phil
  2. Phil Allison

    Phil Allison Guest

    Make that Lexpro brand - damn spellchecker took over !

    .......... Phil
  3. JM

    JM Guest

    That approval number is only in relation to its c-tick compliance, it may
    burn your house down, but there won't be any interference on your tv in the

  4. Phil Allison

    Phil Allison Guest

    ** Hitting a nail on the head is not in the same league as driving
    nails into someone's coffin.

    ............ Phil
  5. People die and they still dont give a shit. Ask QLD's GRAVES (or whtever
    they are called) and they will tell you how to fix the problem. Then
    everyone will complain because they cant get their product certified, just
    like the QLD electrical laws.....blah blah blah..
  6. google is your friend. BITCH
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