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Sharp TV 1984 model 20J81C - fuse blown.

Discussion in 'Electronic Repair' started by derek, Jul 6, 2004.

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  1. derek

    derek Guest

    The main power supply fuse has blown and I'd like to fix this myself
    if I can find the components at fault. It had a burning smell at the
    time it blew, however apart from the fuse itself I can find no signs
    of burned caps, diodes or resistors etc. I have tried to find a
    schematic in the library RCA guides but can only get one for model
    20D74C, however this power supply schematic does not seem to be quite
    the same as my set. Does anyone know which guide number would contain
    my model(20J81C)?
    I have some electronics tech experience but am not a TV technician and
    lack any equipment such as a scope or variac supply; I do however have
    an isolation transformer - only 250VA, would this suffice? So far I
    have used the series light bulb technique; at first the lamp is bright
    but after a minute or so it dims and then starts on and off, about
    once a second with a clicking sound coming from either the main filter
    cap C706 (470micF) or the neighbouring HOT (T602).
    At this time the voltage across C706 rises from 40V to 80V - with the
    lamp still in series.
    Can anyone suggest likely components to test, and how exactly with
    only a VOM?
    In the meantime I'm off to buy a new set but still want to crack this!
    Reply only to the NG please.
    Thanks, Derek
     
  2. Art

    Art Guest

    SAMS Photofact should have a cross reference for your 20 year old Sharp TV.
    The burning smell you refer to may be from the LOPT, Yoke, or other device
    within the set. Suspect possible problems within the deflection and power
    supply circuits. Main situation you may encounter is the availability of
    components for a set this old, especially from Sharp. IMHO.
     
  3. RonKZ650

    RonKZ650 Guest

    The Sharps of this vintage had a big problem with high voltage transformers
    going bad. My guess is the transformer is bad, shorting the horiz output
    transistor then blowing the fuse.
    Rom
     
  4. b

    b Guest

    Derek,

    Good on you for wanting to have a go at saving this set, but I have
    been there, done that in the past, and I have to say that any old set
    like this, having a power supply or line output stage problem (i.e. a
    serious fault) is simply not worth investing time and money in. You
    could end up spending hours repairing the power supply only to find
    that some other critical problem , say, the yoke or Horizontal output
    section immediately causes it to go up in smoke again.
    Save your time and money on this one. Ditch it. After all, you've had
    your money's worth out of the old girl ;-)
    Ben
     
  5. derek

    derek Guest

    Thanks guys; regretfully I think you are right about the probable
    fault(s) and the impracticality of repair. It relates to that other
    post about the future of TV repair doesn't it - very sad. I hate this
    throw away society!
    Oh well - I'm not going to waste money on any rapidly obsolescing
    high-end product when I rarely watch TV. Thinking of a cheap
    Sanyo,Sylvania or something called Prima (Chinese I guess?)
    Derek
     
  6. derek

    derek Guest

    Thanks guys; regretfully I think you are right about the probable
    fault(s) and the impracticality of repair. It relates to that other
    post about the future of TV repair doesn't it - very sad. I hate this
    throw away society!
    Oh well - I'm not going to waste money on any rapidly obsolescing
    high-end product when I rarely watch TV. Thinking of a cheap
    Sanyo,Sylvania or something called Prima (Chinese I guess?)
    Derek
     
  7. derek

    derek Guest

    Thanks guys; regretfully I think you are right about the probable
    fault(s) and the impracticality of repair. It relates to that other
    post about the future of TV repair doesn't it - very sad. I hate this
    throw away society!
    Oh well - I'm not going to waste money on any rapidly obsolescing
    high-end product when I rarely watch TV. Thinking of a cheap
    Sanyo,Sylvania or something called Prima (Chinese I guess?)
    Derek
     
  8. b

    b Guest

    Derek,

    If you don't want to spend a lot of money on a Tv, I would advise
    against going for the supermarket/el-cheapo new sets- they will almost
    certainly develop some problem, usually immediately after the warranty
    expies :-(. If I were you ,I would look at investing the same amount
    of cash (or less!) in a good name brand second hand one which is not
    too old (ie. less than 10 yrs!) (from a reliable retail source if
    poss.).

    For a set such as a Sony, JVC, Philips etc, there will be far more
    technical support and its common faults are already known to the
    repair trade. That way, if anything does go wrong, you're not left in
    the lurch and you'll likely see more life out of your purchase. Try
    posting here for recommedations for reliable used models (don't forget
    to say what part of the world you're in!) Here in Europe, Philips
    ITT/Nokia and Grunding (RIP!) are amongst the best used buys and easy
    to get spares for (IMHO)

    Good luck
    Ben
     
  9. Chaos Master

    Chaos Master Guest

    derek said:
    Get a TV from a known brand like Sony, Philips...
    You will get more TV for what you spend.

    []s
     
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