Re: gEDA-user: Any TV repair gurus lurking?

[Greg Cunningham <greg@xxxxxxxxxxxxxxxxxxxx>]

On Thu, 2007-12-20 at 20:46 -0500, Stuart Brorson wrote:
> Back when dinosaurs roamed the earth, I used to fix TVs in a TV repair
> shop.  Maybe I remember some of what I knew then, but the jury is out
> on that one.
> 
> I'd take a look at the driver transistor for the vertical oscillator,
> or any of it supporting components.  It sounds like the vertical sweep
> osc is having a hard time producing a nice, solid saw-tooth wave.
> Putting a scope probe on it would be a good idea.
> 
> FWIW, the horizontal oscillator is often the culpret in these bad
> sweep problems, so take a look at it too, using the scope.
> 
> HTH,
> 
> Stuart
> 
Dinosaurs eh?.... Noah was my regular customer... Never got that depth
sounder going for him... Might have missed that mountain if I did...

also do a visual of the electros around the vert linearity/feedback
area.  Look for a convex top (indicating excess pressure).  If the top
is not flat then it has probably blown out electrolyte. If there are any
N.P caps there I would check them for esr.
-- 
Greg (who also spins anti-clockwise)

> 
> On Fri, 21 Dec 2007, Peter Clifton wrote:
> 
> > Hi,
> >
> > I'm fixing (or trying to) a TV for a friend, and wondered if anyone had
> > any wisdom relating to the following symptom.
> >
> > This is a Sony BE-3D chassis, and exhibits an intermittent fault. When
> > its doing it, the picture is still visible, but collapsed (jitteringly)
> > upwards towards the top of the screen. It doesn't stay collapsed for
> > particularly long. The sections of image which collapsed upwards also
> > narrowed horizontally, leading to a tapered looking screen
> > ---------------
> > |\           /|
> > | \         / |
> > |  \_______/  |
> > |             |
> > ---------------
> >
> > (Although this diagram probably exaggerates it somewhat).
> >
> > None of the obvious supply caps tested for bad ESR on my meter (main PSU
> > cap, the various secondary side PSU caps including B+, the flyback
> > derived 200V supply etc.) Even when raster / scan has been lost
> > completely, sound works fine. At one extreme I saw in person today, the
> > vertical collapse left three horizontal lines (R,G,B) separated by an
> > inch or so on the screen towards the top. No picture was visible (and I
> > turned it off).
> >
> > I know this set has a common fault with flyback transformers failing due
> > to internal arcing. I almost convinced myself this was probably the
> > case, but now I'm not so sure. Could it cause the symptom? (It usually
> > supposed to trip the sets overcurrent protect on the B+ line and shut
> > down H drive, throwing the set into standby though - which it didn't
> > seem to do for me today).
> >
> > Unfortunately its been several years since I last fixed a TV, and I
> > don't have my handy box of bits for insulated prodding / light-bulb
> > inserting / freezing / HV testing. I don't even have an oscilloscope
> > here (although I could borrow one from the lab). I'm working with
> > multimeter and ESR meter. I do have the schematics and service manual
> > though, which is a big plus.
> >
> > Best wishes,
> >
> > -- 
> > Peter Clifton
> >
> > Electrical Engineering Division,
> > Engineering Department,
> > University of Cambridge,
> > 9, JJ Thomson Avenue,
> > Cambridge
> > CB3 0FA
> >
> > Tel: +44 (0)7729 980173 - (No signal in the lab!)
> >
> >
> >
> > _______________________________________________
> > geda-user mailing list
> > geda-user@xxxxxxxxxxxxxx
> > http://www.seul.org/cgi-bin/mailman/listinfo/geda-user
> >
> 
> 
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-- 
Greg Cunningham
mailto:greg@xxxxxxxxxxxxxxxxxxxx



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