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Fusible resistor selection

Discussion in 'Electronic Repair' started by Russ_Verdon, Apr 15, 2006.

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  1. Russ_Verdon

    Russ_Verdon Guest

    Hi, I just fixed a 19" monitor rescued from the kerb (LICOM N9054LP), and I
    got there before the annoying man who goes aroung cutting off all the cables
    from appliance did!

    Horizontal but no vertical. The Vertical chip was TDA 0472 (couldn't get any
    data).

    The obvious fault was an overheated R501 fusible resistor probably a 1W
    size. If feeds the chip with 15V as per the diagram. Its value changed quite
    dramatically when you flexed the leads from about 60R to hundreds of ohms.
    My problem is that the heat had caused the colour bands to change colour and
    were undecipherable.
    My question is what is the method for calculating a value for these
    protection resistors? I assume we want to minimise Voltage drop and have the
    resistor run within its rating. What base load would you run through the
    resistor? I ended up with a .68ohm with .6volts dropped across it. This
    seemed to restore vertical. The resistor thus dissipates .5W. IS this ok?

    15V supply
    ______|
    __| /
    | \e--------^^^^^^------ pin2 /TDA0472
    NPN _|_ R501 _|_
    __ _ _
    |__________ |
    GND

    Regards

    Russell
     
  2. Guest

    Russel, your calculations seem close enough and your final selection of
    a .68 ohm 1 Watt resistor seem to be quite plausible.
    Run the television for a couple days and make frequent checks to make
    certain than nothing overheats.
    Nice rescue from the curb.
    electricitym
    ..
    ..
     
  3. Chance

    Chance Guest


    I'd find that guy and beat him. "Kerb" side shopping is the best, even
    I can afford the prices!!!
     
  4. Russ_Verdon spake thus:
    I'm curious about this part of the story: who is this guy, and why does
    he go around cutting off cords from potentially good appliances? Is this
    some kind of official function? or is he just an asshole? What
    municipality is this?


    --
    Pierre, mon ami. Jetez vous une plus de Scientologiste
    dans le vat de l'acide.

    - from a posting in alt.religion.scientology titled
    "France recommends dissolving Scientologists"
     
  5. 3T39

    3T39 Guest

    Hello, David!
    You wrote on Sat, 15 Apr 2006 11:12:37 -0700:

    DN> Russ_Verdon spake thus:

    DN> I'm curious about this part of the story: who is this guy, and why
    DN> does
    DN> he go around cutting off cords from potentially good appliances? Is
    DN> this
    DN> some kind of official function? or is he just an asshole? What
    DN> municipality is this?



    The same thing happens at the recycle centre where I salvage a lot of my
    stuff, (A different man though I think, just the same job) The basic reason
    is the connector wire is recycled seperately and also it makes stacking
    easier ( when your dealing with dozens of TV's , VCR's etc the dozens of
    wires become entangled)


    With best regards, 3T39. E-mail:
     
  6. Russ_Verdon

    Russ_Verdon Guest

    Hi, I think this guy collects the wire for selling as scrap copper. It is
    all he takes. I saw him once, he just uses a knife to hack through the
    cables, be it power cords, signal cables from monitors or anythimg else.
    I have lost count of how many cords I have had to attach to scavanged
    equipment to test .

    Regards Russell

    PS I got a 21 inch monitor off the kerb today, thankfully it had an IEC
    socket and separate signal cable. It even goes( just a tweak of the screen
    control and focus required.)
     
  7. It's amazing how people (even supposed technicians) have been
    brainwashed into thinking that most electronics isn't worth repairing,
    or cannot be repaired. It's sad, actually...

    Tom
     
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