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

[Peter Clifton <pcjc2@xxxxxxxxx>]

On Fri, 2007-12-21 at 01:32 +0000, 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
> ---------------
> |\           /|
> | \         / |
> |  \_______/  |
> |             |
> ---------------

Thinking out loud a little..

collapsing towards the centre could indicate raised EHT, but this
doesn't really explain why its only happening towards the bottom of the
image. The image didn't seem to get any dimmer / brighter, so beam
current is presumably not going crazy.

The vertical problem is asymmetric, so might indicate a glitch in either
the + or - 15V supply to the vertical drive amp. Those are derived
straight off the flyback, so either not enough energy is getting into
the circuit (dying B+?), or something is shorting it down
intermittently?

What kind of symptoms would a bad yoke coil contact give (either H or
V?)

Any guru style know-how / deduction would be much appreciated.

-- 
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!)



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