Re: Replaced HOT now what?!
From: Sam Goldwasser (sam_at_saul.cis.upenn.edu)
Date: 07/23/04
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Date: 23 Jul 2004 08:17:41 -0400
"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.
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