Sharp Aquos lc-70le650u - Hissing sound from main board

[twikii]

I've got a pretty loud hissing sound that I think is coming from my TV's main board. This sound is constant and doesn't seem to change once the TV has warmed up. It is there when the TV is on and when it is in standby mode. The TV is working, but the noise is loud enough that I can hear it even when it is playing audio. Does anyone know what the issue is and how I might be able to fix it?

[budm]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

Did you open up the TV and actually listen closely to hear where the noise is coming from? If you lightly press on the boards, does the noise change?
Pleas upload the pictures of the whole backside of the TV showing all the boards.

[Davi.p]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

I think that type of sound usually borns on a coil, it is one from a dc_dc smps or the ones from the audio amp , maybe there is one with the cracked ferrite. But since it is on standby the field is restricted, audio amp cannot be, one one in the standby supply rail.

[twikii]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

Thanks for the response! Attached is an image of the full backside of the TV, the main board, and the component that I think is making the noise. Is this a coil? It's a little hard to isolate the noise and tell which component is making it, even when holding a cardboard tube up to my ear, but I'm pretty sure it's that little guy. Tapping on/pressing on the component doesn't seem to change the noise, though sometimes it will have a clicky noise that sounds a little bit like a hard drive.

[Davi.p]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

That is not what it is usually called mainboard, that is power supply, the item is a standby supply transformer, it is useful to check for high ripple in the electrolytic capacitors in the area, using an oscilloscope or maybe a frequency meter, or check their esr.

[budm]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

That transfomer has ferrite core with two half are jointed together, so look real close at the two joints to see if they have a gap or the core is loose.
The TV functions fine, correct? and nothing change on the screen when it makes clicking sound either, right?

[twikii]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

I don't see any gap between the joints, and the core looks good to me. I tried tapping it because I read somewhere that can sometimes help, but it didn't. I'm not sure what you mean by checking for ripple in the capacitors. I borrowed a friend's multimeter and tested some of the components, but I don't really know what I'm doing. Is there something I could safely put on the noisy component to quiet it down? Is the component something I could replace fairly easily by soldering on a new one? Or would it be best/easiest to just replace the whole board?

[Davi.p]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

you will not find the right part on sale, this is a custom part, those gaps are usually covered by glue, i suggest you to get a hot glue gun and glue the ferrite around against the pcb.

[twikii]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

Thanks for the info! If I am understanding correctly, I should try putting glue around the base of the component - where the red line is?

[Davi.p]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

yes.

[twikii]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

I put a good amount of glue around the base of the component, but it didn't resolve the issue. Is it ok to put glue on top of it, too?

[R_J]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

Start by replacing the two small electrolytics C7907 and C7918. It could be the noise is caused by the standby ic not operating properly and the waveform is a bit erratic.
You could also replace C7303, C7950A & B, the standby output voltage caps

[Davi.p]

Re: Sharp Aquos lc-70le650u - Hissing sound from main board

Don't waste money/time, if you press a piece of sponge on it when it is working and it makes no changes the the glue is not right, you can take a plier and press very gently the two ferrite halves one against to other, if it doesn't change i guess there's another part that makes the noise.