TV problem - noisy flyback transformer. gaffa tape OK?

[Deluks]

Ok we don't have a proper electronic forum but this is close enough.

My gf has a wharfedale tv, from Argos via eBay. Lookin inside it's actually made by in Poland by Thomson. Apparently Wharfedale sold off the name a few years ago and loads of cheapie hifi/tv stuff appeared under the Wharfedale name. So to anyone thinking that it's a solid brand name think again, Although the speaker division is still as good as it's always been afaik.

Anyway the tv gives out a high pitched screech after a few minutes of operation. Some googling on this led me to believe it was the flyback transformer (or line output transformer)

So knowing nothing at all about the inside of a tv, I took the back off ...located the offending flyback and managed to kill the noise by touching it with a wooden spoon.

My gf wants the wooden spoon back cos it's stir-fry tonight, so my question is (for all you tv repair experts) can I gaffa tape the side of the flyback without any risk of overheating/melting etc? A thin strip couple of inches long (on the thin steel bar running up the side) should solve it but I wanna be sure it's safe.

For all those about to suggest I try it and see, I want to eat the stir-fry later, not become it
So replies from knowledgables only please. Or anyone with a clue.

Ta!

 

[Chri5]

Under no circumstances put anything on the transformer that could cause combustion, that includes tape, glue, rubber.

Could you not google the transformer and order a replacement?

If it's resonating within the transformer that is the only really sound fix.

How did the spoon stop the noise, was it due to weight on the transformer or using the spoon to lever the transformer away from the mountings?

You could get some high thermal heat washers (try a plumbers merchant or RS Components) and remount the transformer, the washers acting as suspension units.

If the transformer stopped due to the weight on it, could you simulate the weight affect with something heavy and non combustible. A bit of pathing stone, ceramic tile, part brick, old kitchen scale weight etc....

Alternatively you could play safe and ask the tv man to sort it out professionally

 

[Deluks]

The transformer doesn't appear to give out much, if any, heat. I'd take a picture but dont have camera to hand.

It looks much like this. The metal bar on the right hand side is inset into the transformer, it appears to be some sort of clip or clamp holding it all together. I just held the spoon against it and it changes the frequency depending on where it is on the bar.

I've just been running the tv with a disposable plastic knife wedged into the recess that the clip sits in, the knife when removed doesn't feel warm.

But I need a more permanent solution.

 

[systemtek]

Do not try to fix it, if you dont know what your doing.

There is no point in swopping it out without knowing why its failed in the first place, and there is no sure thing that it is the part you suspect is at fault either. Take it to a TV repair shop to get it looked at.

LOPT's can be quite expensive to start with, you could replace it and it will fail again if you dont know why it failed in the first place.

It could be a dry joint somewhere else on the board that is been affected when you push the LOPT with something, capacitors etc are very common for this.

 

[Deluks]

I have ruled out the idea of replacing it. I know my limitations with electronics, and this amounts to nothing more than prodding about with a wooden spoon

I am almost certain it's not a dry joint elsewhere. It only takes the lightest touch to stop the noise, not enough to affect any other part of the circuit board, it's definitely the flyback transformer. Plus I can find no reference to dodgy caps causing a high pitched whine. It's definitely not in the audio circuit as it happens when the tv is muted.

the plastic knife I wedged in there is only in the recess by about half a mm, you can blow on the knife, it falls out and the noise comes back. Something in the flyback (is flyback tf an american term?) is resonating/vibrating and I need to stabilise it. Other than this problem the tv is perfect.


I've read than rtv silicone will help, I've no idea where to get this from locally so will any other silicone substitute? I've a shedful of glazing, acoustic, firemate, standard and every other type of silicone and sealant. Or how about normal glue, bearing in mind that this component is giving out little or no heat.

 

[bernardgreen]

A drop of two part epoxy resin should be OK. Press it into where the plastic knive blade was.

It sounds ( scuse pun ) that the bracket is slack and hence able to vibrate due the magnetic field.

 

[systemtek]

I have ruled out the idea of replacing it. I know my limitations with electronics, and this amounts to nothing more than prodding about with a wooden spoon

I am almost certain it's not a dry joint elsewhere. It only takes the lightest touch to stop the noise, not enough to affect any other part of the circuit board, it's definitely the flyback transformer. Plus I can find no reference to dodgy caps causing a high pitched whine. It's definitely not in the audio circuit as it happens when the tv is muted.

the plastic knife I wedged in there is only in the recess by about half a mm, you can blow on the knife, it falls out and the noise comes back. Something in the flyback (is flyback tf an american term?) is resonating/vibrating and I need to stabilise it. Other than this problem the tv is perfect.

I've read than rtv silicone will help, I've no idea where to get this from locally so will any other silicone substitute? I've a shedful of glazing, acoustic, firemate, standard and every other type of silicone and sealant. Or how about normal glue, bearing in mind that this component is giving out little or no heat.

The LOPT is one of the heavy components on a PCB, what you say is wrong, how many times i see and hear this. If there is a hairline crack on the pcb or a dry joint somewhere (80% are not visiable to the human eye) it can affect the board when you push the biggest thing on it the LOPT.

You can find no ref to dodgey caps causing this, ask any electronics engineer and they will explain how capacitors work and how they can "wine" some times quite loud, a LOPT can make sound when faulty yes, but why ? Has a componet failed feeding it, maybe not failed directly but when under load, generally a capacitor for such fault. Or you could be correct and its just the LOPT. If you attempt to fix it hope for the best thats all i can say.

I personally wouldnt use RTV or any form of glue to hold the LOPT in place as a repair. Spend the cash and find out whats wrong.

 

[sm1thson]

I know my limitations with electronics, and this amounts to nothing more than prodding about with a wooden spoon

I am sure (/i hope) you already know this but just in case-

be careful with the back off the TV as the tube is basically a massive capacitor that stores lots of energy long after it has been turned off. also unplug (not just turn off) the TV when working on it so the voltages inside arent referenced to ground.

 

[bernardgreen]

As the set appears to work normally when "screaming" I am assuming there is no electrical fault being "repaired" by the wooden spoon and the scream is a slack bit of metal.

as the tube is basically a massive capacitor that stores lots of energy for a long time

For a very long time. Yesterday I took a belt while repairing an oscilloscope that had been turned off for 24 hours.