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Philips TV Repaired with LOPT -> Causes?

Discussion in 'Electronic Repair' started by Peter Clifton, Feb 16, 2004.

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  1. Hi, I would like to enquire if anyone can give me some advice about a repair
    I did for a friend recently.

    The TV was a Philips 14PV182/05, which had a tripping powersupply.

    I tested most of the electrolytics with my ESR meter, and supprisingly they
    all read good.

    I tested the HOT -> good, but the set worked with it removed. (Sound + VCR)

    I isolated all the secondary supplies derrived from the LOPT, but the set
    still tripped (HOT in place).

    So I presumed a faulty LOPT. This was confirmed by rudimentary ring testing
    on my oscilloscope.


    I replaced the LOPT with an HR equivilant, and the TV now appears to be
    working fine. My question is, weather I should be looking for an underlying
    cause for the original LOPT to fail. I did notice that there was some high
    frequency sound coming from the TV (Audible with the TV volume turned right
    down, and the cover off) - after I replaced the LOPT. This makes me wounder
    if everything is A-Ok, but I'm aware that transformers / capacitors can
    sometimes make some noise when running normally.

    Do LOPTs just fail on their own, or are they usually 'caused' to fail by
    another part? I've seen a cople of references to similar symptoms in this TV
    (PSU tripping) being fixed by just replacing the LOPT.

    Please note that I don't do this for a living or anything, I'm an electronic
    engineering student, and only have a few years worth of experience fixing
    the odd monitor / TV / SMPS etc. My theoretical knowledge isn't too bad (I
    think), but I lack the experience of someone who comes across these faults
    day after day.

    Thanks for you help

    Peter Clifton
     
  2. Alain Beguin

    Alain Beguin Guest

    Peter Clifton schreef/a écrit/wrote in/dans/in
    They fail on their own, Peter. Especially in those sets. We replace a
    few every week.
    The quality of those transformer has dropped dramaticaly.

    Sometimes the line output transistor has to be replaced as well and a
    little blue capacity, close to that transistor.

    Greetz,
     
  3. Thanks for that - it makes me feel better about the job I did.

    Presumably, if the cap or the HOT need replacing then it would show some
    visible sign of it when I powered the set up again.
    (I hope anyway)

    My friend has her TV back now, but if anyone thinks there is still cause to
    be concerned or investigate further, I could ask to look at it again.

    I love to repair things (and hence work for free - I wouldn't claim to have
    a high enough competence or give a high enough success rate to charge like a
    pro), but I can see why repairing televisions is becoming uneconomical
    nowadays. For a little more than the cost of parts and labour, people can
    simply buy a new TV which may (or may not perhaps) have more lifetime in it
    than a repaired 6yr old set. The new LOPT was about £20, and a new set was
    only £100. Once you add in labour, its getting to be a close call.

    Many thanks for your advice

    Peter
     
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