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From: Sylvia Else on 16 Oct 2009 21:31
Sylvia Else wrote:
> This television displays a strange image and sound distortion just after
> it's been turned on, as shown in this 5 second video.
>
> http://www.youtube.com/watch?v=usQFxTJ04s4
>
> It may do this several times, and, rather disconcertingly, seems to be
> slowly getting worse.
>
> Note - the slight flickering is an artefact of the video recording.
>
> I'm using a computer output to show the fault, but I get the same
> behaviour on broadcast channels if the computer is completely
> disconnected, and turned off.
>
> I suspect a warming up effect. Any ideas?
>
> Sylvia.

Just a followup on this. The problem got gradually worse, to the point
where it continued for minutes after turn on.

Which gave me a chance to see where it was arcing. Turned out to be
underneath the circuit board, due to a fractured solder joint, and hence
only visible when I had the back of and bent down to see that area. Once
I knew where to look, it was obvious that the joint was broken. 30
second soldering job, and now it's good as new.

The surprise is more that it was working at all.

Special thanks to Jamie for the correct diagnosis of arcing.

Sylvia.
From: Sylvia Else on 17 Oct 2009 04:39
Sylvia Else wrote:
> and now it's good as new.

I may have spoken too soon. Certainly the arcing issue is resolved.

But now the picture colours make it looks as if the tube is in need of a
serious degaussing. Even the television's own set up captions vary in
colour across the screen.

If I understand things correctly, this cannot be a consequence of my
soldering technique, but has to be the result of something moving when I
tilted the TV over to get access to the circuit board.

Either that, or there is previously unnoticed mucking great magnet
underneath my floor boards.

Any thoughts?

Sylvia.


From: Sylvia Else on 17 Oct 2009 05:31
Sylvia Else wrote:
> Sylvia Else wrote:
>> and now it's good as new.
>
> I may have spoken too soon. Certainly the arcing issue is resolved.
>
> But now the picture colours make it looks as if the tube is in need of a
> serious degaussing. Even the television's own set up captions vary in
> colour across the screen.
>
> If I understand things correctly, this cannot be a consequence of my
> soldering technique, but has to be the result of something moving when I
> tilted the TV over to get access to the circuit board.
>
> Either that, or there is previously unnoticed mucking great magnet
> underneath my floor boards.
>
> Any thoughts?
>
> Sylvia.
>
>

So I pulled it apart again, checked for anything loose in the stuff
attached the tube - there wasn't - and put it back together...

.... and it's fine.

While I was getting a handle on where exactly it was arcing, I was
running it screen face down (on a soft surface), for a while, so the
Earth's magnetic field would certainly have changed relative position.

Could it be that all it needed was a couple more cycles of its own
degaussing?

I'm pleased that it's OK, but I don't like not knowing why.

Sylvia.
From: William Sommerwerck on 17 Oct 2009 07:30
> Could it be that all it needed was a couple more cycles
> of its own degaussing?

Likely. It also might be that the shadow mask got warped, and repeated
handling knocked it back into shape.


From: Sylvia Else on 20 Oct 2009 19:16
William Sommerwerck wrote:
>> Could it be that all it needed was a couple more cycles
>> of its own degaussing?
>
> Likely. It also might be that the shadow mask got warped, and repeated
> handling knocked it back into shape.
>
>

Just for the record, and for the benefit of anyone who comes across this
in the archive, further online research revealed that part of the
purpose of the degaussing process is to *magnetise* the shadow mask in
such a way as to cancel out the Earth's magnetic field in the space
between the mask and the screen. This is the reason the shadow mask is
made of a magnetisable material (which otherwise would seem a strange
design choice).

So my experience can be adequately explained by the fact that I powered
the TV up while it was in a completely different orientation from
normal. It was then entirely possible that this would take several
degaussing cycles to undo properly once I had the TV back in the normal
position. The situation was further confused by my failure to realise
that this model only degausses when powered up from the mains, and not
when going from standby to on. It's necessary to power it down
completely for a while before powering it up again for it to do its
degaussing.

So I guess that's that.

Sylvia.
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