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In-rush resistor failed

Discussion in 'Hobby Electronics' started by RMD, Nov 3, 2011.

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  1. RMD

    RMD Guest

    Hi All,

    I just thought I'd say this LG DVD/VCR unit discussed below is still
    working fine with the new in-rush resistor installed.

    Ross




    Hi All,

    A friend of mine has an LG DVD/VCR combination unit which suddenly
    went completely dead.

    These units are getting pretty hard to buy these days, so I lent her
    an old VCR of mine so she could use her VHS tapes.

    It seemed to me it was likely a power supply problem, and so it proved
    to be.

    A 2.2ohm 2W current in-rush resistor right at the mains input had gone
    open circuit. I went down to Jaycar and bought a 5W resistor for $0.40
    and once I installed the new resistor the unit sprang into life again.

    Checking voltages around the power supply then the voltages are
    generally what I would expect to find. Nothing looks damaged or
    overheated anywhere. No bulging capacitors either.

    However, it has been my experience that repairing these switching
    power supplies is never quite as straightforward as it might seem to
    be in the first instance. Most of the components are fairly highly
    stressed and one weak sister can fail other components and the weak
    sister survives itself.

    Anyway, while I guess the inrush resistor might fail open like any
    resistor might rarely fail this way, is there anything else I ought
    feel suspicious about if this in-rush resistor fails?

    And just by the way I don't really understand why this resistor needs
    to be 2W either. VCR's usually only use about 5-10 watts or so, so it
    is hard to see where 2 watts of heat comes from in the 2.2 ohm
    resistor. Or is this resistor really being sized for a voltage rating
    and the 2W rating just comes with the voltage rating territory?

    Ross
     
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