Re: Replaced HOT now what?!

From: Sofie (sofie_at_olypen.com)
Date: 07/23/04 

Date: Fri, 23 Jul 2004 12:15:57 -0700

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
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"Chistopher Parsons" <ccparsons@fastmail.fm> wrote in message
news:cJ9Mc.81809$Np3.3890717@ursa-nb00s0.nbnet.nb.ca...
> 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.
>
> "Sam Goldwasser" <sam@saul.cis.upenn.edu> wrote in message
> news:6w4qnyc3yy.fsf@saul.cis.upenn.edu...
> > "Chistopher Parsons" <ccparsons@fastmail.fm> writes:
> >
> > > 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.
> >
> > 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.
> >
> > --- sam | Sci.Electronics.Repair FAQ Home Page:
http://www.repairfaq.org/
> >  Repair | Main Table of Contents: http://www.repairfaq.org/REPAIR/
> > +Lasers | Sam's Laser FAQ: http://www.repairfaq.org/sam/lasersam.htm
> >         | Mirror Site Info:
http://www.repairfaq.org/REPAIR/F_mirror.html
> >
> > 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.
> >
> >
>
>

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