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Replaced HOT now what?!

Discussion in 'Electronic Repair' started by Chistopher Parsons, Jul 23, 2004.

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  1. So I had a defective Damper-Diode-Horizontal-Output-transistor ...
    .... replaced it and a blown fuse and the dead TV
    came on ... it didn't before even with a new fuse. ;-)

    The picture then looked fine except it used to shrink and
    grow both on the horizontal and vertical. I replaced
    a few of the capacitors with no change.

    I noticed a kind of burnt smell coming from a large
    transistor with "warning high voltage" on its large heatsink
    in or near the power supply section. It's a BU508A (NTE2300).

    A Horizontal Output transistor?!! Another one?
    I just replaced a D1398 (NTE2302) over near the
    flyback! What's another Horizontal Output transistor
    doing over near the power supply? It's a 27" TV.

    Anyways, I check the BU508A (NTE2300), the one
    near or in the power supply section and it checks fine
    on the multimeter. I thought I smelled a burned kinda
    smell coming from it.

    AND while I had it plugged in and on and running with
    the screen size changing sparks or arcs (whatever you
    want to call it) occurred from the Collector and Emitter
    legs. I immediately unplugged it.

    OK. So now I'm stumped. TWO horizontal output transistors?
    One of which checks fine on the multimeter yet I'm sure I smelled
    it kinda burning (when the TV was on) and I SAW sparks coming
    from its Emitter/Collector area on the PCBoard and it checks fine?!

    It must be breaking down in circuit when it's on and working.
     
  2. SPOCKFOO

    SPOCKFOO Guest

    LET IT COOL DOWN
     
  3. Check the soldering. No way you'd get sparks from a transistor
    otherwise.

    One is the HOT, the other is probably a power regulator.

    Get the Sams' or other service info. If that second transistor is
    not overheating because of bad connections, probably due to other
    parts being defective.

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    Important: Anything sent to the email address in the message header is ignored.
    To contact me, please use the feedback form on the S.E.R FAQ Web sites.
     
  4. I had initially checked the solder connections and they
    looked and checked (continuity) good. The Emitter
    and Collector legs each have a round insulating ring
    around them; my guess to keep high voltage arcing
    from occuring. [just a guess on that]

    Whether that transistor was on the way out,
    [ie. slight burning smell and changing picture size]
    or the arcing did damage I won't know for certain.

    I do know for certain that it's a shorted dead transistor
    now and will have to wait to replace it before continuing
    with my TV repair.

    <sigh> and alas .... and sigh again.
     
  5. Sofie

    Sofie Guest

    Christopher Parsons:
    The round rings around the legs of the HOT are not for insulation but rather
    they are ferrite beads that provide the function of a RF choke to suppress
    parasitic oscillations. Make certain that they are replaced as found
    originally.
    --
    Best Regards,
    Daniel Sofie
    Electronics Supply & Repair
    - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -


     
  6. Art

    Art Guest

    Unless he is referring to the grommets on the pcb to which the part is to be
    physically connected to and securely soldered before applying power,
    there-by assuring the component leads do not arc and spark to the grommets.
    ??
     
  7. Sofie has it. They're more like a ceramic.

    So, they're ferrite beads? I was gonna put
    them back on the replacement transistor and
    now I know why. Great stuff. Thanks.

    - Chris

     
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