Recurrent "snapping white line" TV prob...advice needed.

[flangemonkey]

Hi.

My aging, but still lovely Sony KV-25F1U 4:3 set has started displaying an unusual problem.

Here's the prob:

It will emit a "snapping" sound from inside the chassis (not out of the speakers, it seems to be fairly near to the rear), accompanied for the most part by a narrow white line shooting horizontally across the image...sometimes, there is no line, but this is very rare, perhaps once out of 50 "snaps" there will be no line.

It "snaps" like this periodically every 5 seconds or so...very annoying.

It looks like it could be something electrical? However, this is coming from a layman, not a qualified TV engineer.

A switch-off and on doesn't seem to cure it, it just does it from the get go.

It used to only do it for the first 10 mins or so after being switched on (disappearing after presumably "warming up") until at least the next time the TV had been turned on from cold.

Now it does it all of the time, from the get go

Anyone know if it's completely up the creek or if it would warrant a repair...and how much it's likely to cost if not too serious?

Cheers in advance...

 

[flangemonkey]

No-one?

 

[bonzobanana]

I'm not an engineer myself but have repaired some tvs on the advice of engineers from various sources on the internet. I had a similar problem with a Pye tv and was told to check for dry joints/solder under the line output transformer. Anyway I opened up the set once it had been disconnected from the mains for a couple of days. Vacuumed it out (it was dusty as hell) and then spotted underneath just one solder connection that looked much duller than the rest. I only resoldered this connection and the set was fine again. Lasted about another 6 months before the push button preset mechanism failed. This is going back to about 97/98 I think. Theres probably about 25% of repairs that can be achieved at home at no expense just by cleaning, checking cables and resoldering obvious dry joints. I repaired a hitachi once that was intermittant and that was only one leg was soldered on a transistor causing it to make intermittant contact. Lived with the fault for about 18 months and one blob of solder was the cure. Just about to throw that set out now. Its still working fine but the picture ain't great

 

[Chris Muriel]

It could be flashover across the spark gap that exists on many TVs.
You would see the source of any flashover with the back off the set , or possibly some arcing around the line output stage.
You could do this carefully in a darkened room.
Do beware , however, because these stages develop about 25 kiloVolts - and take off your watch before you even remove the back from the set.
If in doubt, leave it to a professional.

NB: If it's a 100Hz set , like my Philips, it may have 2 separate line output stages - one for 50 Hz, one for 100 Hz.
Chris Muriel, Manchester.

 

[GaryB]

Chris's description sounds about right. It sounds like HT arcing over. This could just be across a spark gap but this is unusual every few seconds. Are you by any chance smokers? If so, the accumulated gunge from cigarettes often collects around the anode cap (which has the 25Kv in it) and causes these symptoms as the HT arcs to the aquadag (the silver coating on the back of the tube).

 

[flangemonkey]

Thanks for the info guys...

It is really pretty intermittent. Some days it will only "snap" a couple of times within a few hours, then on others it will be doing it every five seconds or so for around an hour or two before stopping altogether until the next time you turn it off/on.

I really don't want to take the back off myself, because I know of the stored voltage these things can hold long after being turned off, and I really don't fancy a crackly "surprise" if I touch anything inside...

We're not smokers, and the place is kept pretty clean IMO, but as the set is getting on for 9 years old, the accumulated gunk/dust could well be to blame.....I could try firing one of those compressed air thingies you use to clean out PC cases into the chassis perhaps if it starts to get much worse?

I really want a new set though, so this would give the perfect excuse, and as soon as funds allow I'll plump for a component-capable CRT I think.