Problem with Sony KV-T25SZ8 TV when turning on

Muting usually occurs in front of the amp. Otherwise if you "kill" the amp it might make some noise as it shuts down/restarts.

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.

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.

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.

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