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Sony KV-2780R Shorted HOT replacement

Discussion in 'Electronic Repair' started by Marc, Oct 19, 2004.

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  1. Marc

    Marc Guest

    I recently acquired a non-working Sony KV-2780R television
    manufactured in 1987.

    I know nothing of the history of this television, but it was one step
    away from the dump...and is an excellent candidate for educational
    purposes...(aka FREE!)

    I pulled the back off, and checked the main fuse, it was ok.

    I plugged it in, and turned it on. I could hear the "on" circuit come
    on, but no sound or picture.

    I then unplugged it and began taking a closer look at the video
    circuitry.

    (the audio portion of the circuitry appears to be contained on a
    separate board,
    probably modular, and probably used on several different models of
    televisions)

    The only "clean" area on the video circuit board was a
    heatsink/transistor sub-assembly located just in front of the flyback
    transformer.

    The heatsink/transistor sub-assembly was just sitting there, loose,
    de-soldered from the board. (all three of the transistor leads, as
    well as the heatsink mountings were de-soldered from the board)

    The transistor (D1497) is shorted out.

    My guess is this: that a repair technician checked the set, and
    determined that, at the very least, the HOT was bad, and the overall
    cost of the repair was too expensive, so the television was not
    repaired.

    Here is my question:

    When the HOT is determined to be shorted, is this symptomatic of a
    larger problem???

    Possibly other parts down stream or up stream (so to speak) shorting?

    Again, any and all help is appreciated,

    Thanks,

    Mark
     
  2. Jerry G.

    Jerry G. Guest

    When the HOT is shorted out, this can be from a drive problem, or there
    is a defective flyback, and or there are defective components on the
    output side of the flyback. Very often in this series of set, I found
    the flyback had to be changed, and or there were problems in the drives
    from the scan gen circuits to the HOT. If the HOT is shorted, there is a
    good chance that some damage to the power supply may have also occurred.

    Considering the age of the set, there is a strong possibility, that
    there will be many electrolytic caps that have become high in ESR from
    their age.

    To service the set, you will have to work one step at a time until you
    resolve all the issues in each area. This is something that cannot be
    predicted over an email.

    I would not look at servicing a TV set a good way to learn electronics.
    You will gain only some familiarity of how TV sets are built, but not
    really a strong learning of the detailed theory of how they and their
    circuits operate.

    --

    Jerry G.
    ======

    I recently acquired a non-working Sony KV-2780R television
    manufactured in 1987.

    I know nothing of the history of this television, but it was one step
    away from the dump...and is an excellent candidate for educational
    purposes...(aka FREE!)

    I pulled the back off, and checked the main fuse, it was ok.

    I plugged it in, and turned it on. I could hear the "on" circuit come
    on, but no sound or picture.

    I then unplugged it and began taking a closer look at the video
    circuitry.

    (the audio portion of the circuitry appears to be contained on a
    separate board,
    probably modular, and probably used on several different models of
    televisions)

    The only "clean" area on the video circuit board was a
    heatsink/transistor sub-assembly located just in front of the flyback
    transformer.

    The heatsink/transistor sub-assembly was just sitting there, loose,
    de-soldered from the board. (all three of the transistor leads, as
    well as the heatsink mountings were de-soldered from the board)

    The transistor (D1497) is shorted out.

    My guess is this: that a repair technician checked the set, and
    determined that, at the very least, the HOT was bad, and the overall
    cost of the repair was too expensive, so the television was not
    repaired.

    Here is my question:

    When the HOT is determined to be shorted, is this symptomatic of a
    larger problem???

    Possibly other parts down stream or up stream (so to speak) shorting?

    Again, any and all help is appreciated,

    Thanks,

    Mark
     
  3. john

    john Guest

    Ok Usually when the HOT in that Model goes
    its caued by bad Flyback Transformer.
    Best to change the Regulator / HOT / Disk Cap off HOT / Flyback.

    kip
     
  4. RonKZ650

    RonKZ650 Guest

    Also the 2SD1497 Sony is no longer available. You need to use the T-9985-664-1
    2SC4927 kit. If you try to order a 2SD1497 you'll get one with the metal back
    and it will not work. Sometimes you get lucky and transistor fixes it,
    sometimes it's the flyback transformer, sometimes the small electrolytic cap
    between the driver transistor and driver transformer.
    Or am I wrong here Leonard? Comments to follow I'm sure.
    Ron
     
  5. Andy Cuffe

    Andy Cuffe Guest


    You will definitely need to replace the HOT and voltage regulator (STR
    something). It's also a good idea to change the electrolytic cap in
    the horizontal drive circuit. I think this is near the vertical IC
    heatsink. You may also need to replace the flyback. You should be
    able to get all these parts from MCM electronics including a generic
    flyback. I wouldn't spend the money on a genuine Sony flyback
    considering the age of this set. The picture tube is probably getting
    weak.
    Andy Cuffe
     
  6. john

    john Guest

    Dont use a Generic in this Model it will FRY.

    kip
     
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