Problem with Sony KV-T25SZ8 TV when turning on

Sylvia Else wrote:
Bob Larter wrote:
Sylvia Else wrote:
Bob Larter wrote:
TonyS wrote:
Bob Larter wrote:
Sylvia Else wrote:

Accumulated dust &/or smoke on the EHT circuitry & the back of the
CRT. Take the back off the TV & see if you can see any arcing.


I would. It most likely needs nothing more than cleaning out all
the gunk.


It's been a long time since I fixed my CRT TVs. But, wasn't it that
the picture expanded when the HV briefly collapsed when arcing? I
can't see this happening in the video.

I would expect the image to shrink horizontally &/or lose brightness
during arcing.


I think there is an, albeit slight, reduction in width. Whether the
brightness drops is hard to say because the colour disappears.

What I find striking is that some scan lines appear to start early,
by an amount of time that is quite consistent.

It's not clear to me whether the noise is coming out of the
loudspeakers, or directly from the interior of the TV.

Try muting the sound then listen for the noises. If it's audible at
all, arcing tends to make a hissing or crackling noise.


Does muting kill the power to the audio output amplifier, or just its
audio input?
Click to expand...
Dunno, but most probably the latter.

--
W
. | ,. w , "Some people are alive only because
\|/ \|/ it is illegal to kill them." Perna condita delenda est
---^----^---------------------------------------------------------------
 
On Wed, 19 Aug 2009 12:08:36 +1000, Bob Larter
<bobbylarter@gmail.com>wrote:

Sylvia Else wrote:
Bob Larter wrote:
Sylvia Else wrote:
Bob Larter wrote:
TonyS wrote:
Bob Larter wrote:
Sylvia Else wrote:

Accumulated dust &/or smoke on the EHT circuitry & the back of the
CRT. Take the back off the TV & see if you can see any arcing.


I would. It most likely needs nothing more than cleaning out all
the gunk.


It's been a long time since I fixed my CRT TVs. But, wasn't it that
the picture expanded when the HV briefly collapsed when arcing? I
can't see this happening in the video.

I would expect the image to shrink horizontally &/or lose brightness
during arcing.


I think there is an, albeit slight, reduction in width. Whether the
brightness drops is hard to say because the colour disappears.

What I find striking is that some scan lines appear to start early,
by an amount of time that is quite consistent.

It's not clear to me whether the noise is coming out of the
loudspeakers, or directly from the interior of the TV.

Try muting the sound then listen for the noises. If it's audible at
all, arcing tends to make a hissing or crackling noise.


Does muting kill the power to the audio output amplifier, or just its
audio input?

Dunno, but most probably the latter.
Click to expand...
Muting usually occurs in front of the amp. Otherwise if you "kill" the
amp it might make some noise as it shuts down/restarts.
 
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.
Click to expand...
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.
 
Sylvia Else wrote:
and now it's good as new.
Click to expand...
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.
 
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.
Click to expand...
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.
 
Could it be that all it needed was a couple more cycles
of its own degaussing?
Click to expand...
Likely. It also might be that the shadow mask got warped, and repeated
handling knocked it back into shape.
 
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.
Click to expand...
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.
 
Sylvia Else wrote:

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.
Click to expand...
Its also why many have a manual degauss button or menu selection.

--
Best Regards:
Baron.
 
You must log in or register to reply here.

Welcome to EDABoard.com

Sponsor

Back
Top