Crackly fizzy (mechanical ?) noise from TV ?

[Jethro_uk]

Our lad inherited out old first-gen LCD HDTV (11 years old). Been fine (lost remote apart) for him for 5 years ...

Now it still works, but when you turn it on, there's a crackling/fizzing sound from the _centre_ of the back. It's definitely not coming from the speakers.

The second I first heard it I thought "capacitor" ?

It's a very light sound - not sharp enough to be arcing. And whatever it is doesn't seem to affect the TV operation. Just be a nuisance.

If I could be bothered to pop round and spend a few minutes investigating, where would the wisdom of uk.d-i-y suggest I look ?

He's already bought a replacement, so this has been relegated to "games console" :)

[charles]

Never having taken one apart I can only guess. These used to use small fluorescent tubes behind the screen to provide illumination. Perhaps there's a dodgy contact on one of the tubes; or perhaps a tube is dying and having difficulty striking.

[Harry Bloomfield]

It happens that Jethro_uk formulated :

Likely the switch mode power supply has begun to age and is whistling and there is some resonance. You could try taking the back off, locating the SMPSU then prodding it gently with something insulated when its running.

[The Natural Philosopher]

Prolly the HT around the backlight. Or something in te PSU.

Not much else takes enough power to make a noise

[John Rumm]

That still may well be an issue ;-)

Older LCD TVs had fluorescent tube backlights, and typically a SMPSU driving them via a step up transformer to get the ~700V DC they required. The most common failure modes being the caps on the output of the PSU, and the transformer itself.

[Jethro_uk]

Hmm

TV screen lights up fine - if it didn't I wouldn't waste a second on the thing :)

[Jethro_uk]

I was kinda thinking something along those lines.

Assuming it's not a Krypton Factor build, I might pop a toolbox in the car next time I pop round.

[Andrew]

It's 11 years old, well past its appointment with the local authority 'recycling' skip, surely ?

[Cursitor Doom]

Yeah, what could possibly go wrong with a bit of prodding around? Even experienced service persons religiously use an isolation transformer when they absolutely have no choice but to work on a mains supplied SMPS live. It's certainly not the sort of job you should be encouraging an ordinary mortal to attempt.

[John Rumm]

While it does not owe anyone anything, there is enough of a chance it can be fixed with 15 mins work, and less than £10 worth of components to make it worth at least popping the back of for a quick poke about I would have said.

[Fredxx]

As long as the OP uses an insulated tool to touch anything I don't see the problem, as long as he has a healthy fear of contact with moderate voltages.

It's not like working on the EHT of an old TV set or on a microwave.

[Brian Gaff]

Backlight inverter insulation breakdown? Brian

[Brian Gaff]

I think we would need to know the make and model as some people probably know what we used to call stock faults on older sets and whether the problem was serious or merely something rattling. I have an old laptop that whines with the lid in a certain position, its the core of the inverter for the backlight resonating at a sub harmonic of the oscillator frequency. I long remember the old 405 line tvs that really did deafen many with their hf line oscillators in some models. Brian

[Terry Casey]

For the first nine years of my working life I worked on live chassis TVs[1] and radios without the use of an isolating transformer.

We relied on the bench positions being earth free areas and that pasted muster for the one and only inspection from a Factories Inspector I encountered in all that time.

Would you expect a field engineer to lug a hefty isolating transformer around with him from house to house?

[1] The vast majority having unpolarised 2-pin mains connectors on the back.

And you know for certain that the OP is an 'ordinary mortal' with no sense of self preservation and the need to adopt safe working procedures?

[tabbypurr]

sounds like arcing, which is an immediate fire risk

NT

[Tim+]

That?ll be he degaussing coils. ;-). Maybe they left them in the design...

Tim

[Jethro_uk]

I am old enough to remember them on CRT monitors.

[Jethro_uk]

That's the vague motivation.

If it was making a noise *and* not working, I'd bin it.

[Jethro_uk]

Yeah, this definitely had a fluorescent backlight. Interestingly it failed to catch a couple of times about 8 years ago (when we had the TV). Turned off, turned on, and it worked .... and the light is *still* working.

[Jethro_uk]

I know how insulation works :)

Anyway, my first thought (backed by the replies to this thread, which I thank all for) is to see how easy it is to lift the actual plastic cover, and have a look and listen without any contact at all. Since it's a noise I'm trying to isolate, there's always a plastic rod to the ear. (My Dad used to have a 2' screwdriver he'd use for listening to engines ....)