Transformer varnish to stop SMPS transformer buzzing?

[tom66]

My Kuro plasma TV has a rather loud buzzing transformer on the SMPS... the buzzing varies with picture brightness. I've located it to be the source of the noise by use of a cardboard tube.

The TV is nearly 5 years old now, I suspect the original varnish has dried up.  I can see they did use varnish on it, because it has a brown tint in areas where it has dried.

Anyone have any suggestions on how to fix this? Preferably without removing or disassembling the transformer. I was thinking of getting some fresh varnish and brushing it around it, hoping it would soak into the windings, but I'm not sure how well that will work.

[SeanB]

Buzzing transformer is more likely a sign of failing caps in the primary side. as the transformer operates at well above your hearing. A buzz will be it varying in sympathy with the much larger mains ripple. Usual checks of the caps is needed for bulging or the use of Crapolytics.

[free_electron]

Bad caps. Transformer duty cycle is off whack.

[tom66]

The buzzing is caused because the sustain boards draw current at about 60 Hz x 28 fields/frame = ~1.7kHz. i.e. the load modulates the current at about 1.7kHz. I am relatively sure the capacitors are all OK. (It has enough of them, plus only the big four - Nichicon, Chemicon, and Rubycon mostly, with the primary caps being Hitachi.) The TV & Vsus section is otherwise fine (steady 210V at full load white, not varying under load.) Normally the transformer should not make this noise. Most Kuro owners start having this problem after a few years.

See picture for the panel sustain waveform for the common electrode drive. Lots of opportunity for noise to leak everywhere. The sustain boards do gently buzz but not very much.

Pioneer did not cheap out on this set...

[What_NZ]

I don't know what this transformer looks like but I recall in the early days watching TV tech's forcing in shims and/or packing the transformer with high temp, two part Epoxy glue. It never looked pretty but it did work.

[Richard Head]

What does this mean? "See picture for the panel sustain waveform for the common electrode drive."

[all_repair]

More than 50% are due to capacitor but not limited to the electrolytic type.  It can also due to mechanical as you said the vanish.  It could be some glue have come loose.  This is earlier to identify by pressing around with an insulator.   For vanish, they do not flow that well and the hollow area that is having the vibration may not be reachable.  Best you can do is to inject as throughout as you can, as the vanish dries up,  tension shall build up and pull on the whole assembly and  likely remove the slag and so reduce the sound.

[tom66]

What does this mean? "See picture for the panel sustain waveform for the common electrode drive."

The waveform shown is what is driven into the plasma panel's common electrode in order to make it light up. The opposite phase waveform (with a few minor differences to the start of the waveform) is applied to the other end, the scan electrode to give the panel ac drive. Light is emitted in one of those 28 middle fields. On any pixels that have been written to, light is emitted from those pixels.  That is where current can be drawn from. A plasma display can't make variable intensity, only on/off. So the image is divided into subfields and the amount of time in each subfield of a varying length codes for pixel intensity.

[Richard Head]

I would be inclined to load the PSU with an external resistive load and see if the noise is still present.
My money is on an electrolytic that has gone low in value, but who knows.

Dick

[PedroDaGr8]

Also, note that Panasonic had a recall for some of the SMPS in certain models. Apparently, the cores could crack and that would lead to loud buzzing noises.

[Richard Head]

A cracked core would produce that exact symptom.

[CrackedCore]

i have exact issue on my kuro plasma, nearly 1o year old,

https://imgur.com/a/a65gzVN

Seems like this(trafo on the pic) is the loudest source of buzzing, is that cracked transformer?
caps dont look bulged,

Is there anything i can do about it?
Zip tie it? Nail polish it, varnish or something like that?

[chris_leyson]

@CrackedCore, surprise surprise it's a TDK transformer. Recently I had to take apart some TDK manufactured transformers to trace the source of a whistle at about the same frequency. A flyback running in burst mode whilst in standby. TDK ECO2020 core with an interleaved primary so lots more tape between windings and the windings become a bit more squishy, sorry couldn't think of a better word. Anyway, no cracked core and very good varnish impregnation between core and bobbin so I don't think it was the core. I did notice that there was very little varnish on some of the windings so I went for loose windings causing the noise. To properly varnish impregnate a transformer you would have to stick it in a small tin of varnish and use a vacuum pump to suck all of the air out, not easy.

[CrackedCore]

Is it a necesity to take this to service the transformer with varnish, or only if the noise is bothering me too much?
Can i take the board out and take it to some service shop to do the professional varnish job for me? Or is there a new transforemr like this one to simply replace it?

There are also some thick  coils that are pretty loud, is it safe to put some transparent nail polish on it by myself to reduce that noise at least?

Could some bad capacitor be the reason for the noise in the transformer?

I could just put some acoustic foam behind the TV to reduce the sound bouncing back at me from the wall

[Andrew Morton]

There are also some thick  coils that are pretty loud, is it safe to put some transparent nail polish on it by myself to reduce that noise at least?

Nail polish contains acetone. Acetone dissolves lots of things, perhaps including the transformer varnish and the insulation on the wires, before it evaporates - while still in solution, those essential insulators might move away from where they are needed.

Does the spec. sheet for the nail polish include any information about its electrical insulation properties? Might it melt at the temperature of the transformer in operation?

[mr.fabe]

This works for transformer windings...

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