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Black screen on power up - noise coming from power supply board

Hi,

I noticed a TV out on the street that had been thrown out. It was near my house, so I thought why not take it and have a look to see what is wrong with it.

Here’s what happens:

Plug power cord into outlet. A very faint sound can be heard coming from one of the components on the power supply board. Power LED is red which likely indicates standby. Press power button and light turns blue (probably indicating ON status). After this, that same component makes a more noticeable constant noise. I can’t really describe it, it’s buzzing or chirping, just a constant sound that doesn’t stop. Screen is pitch black. No backlight or anything like that can be seen upon power up.

If the board is just plugged into the mains, it makes no sound at all. As soon as the main board gets plugged in, it makes a faint sound on standby mode and gets louder if I press the power button.

Block Image

The component that makes the sound is circled in red on the screenshot.

I’m suspecting it’s either the main board or the power supply board. Any idea what it might be? What does that circled component do? And what would make it produce a noise?

My first guess was since the power supply board is producing the noise, it has to be that board. However, it could also be something the main board is doing. I’ve read some threads of similar issues and it’s turned out to be the main board, only difference is I see power LEDs.

Appreciate any help.

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I seem to be getting power to the main board, but there's still no image on the screen. I did a backlight check by shining a bright light at the screen - nothing. I connected external speakers and plugged my laptop into the TV via HDMI. The sound cuts on the laptop and seems to move to the TV. However, no sound comes out of the speakers.

Power board seems to ne giving expected voltages.

Here's the sound produced by the marked component: https://vocaroo.com/1lRGnczyvSMA

I checked voltage at the LED+ part of the cable and the multi-meter shows a stable 212.9V.

The BK/ON part of the cable that goes from the power supply to the main board reads 5.22V on both ends.

Main heatsink on main board is not warm. It seems cold or near enough room temperature. The ICs surrounding the heatsink are also not warm.

Anyone have any ideas what else to check?

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It turns out there is an image under my phone's flashlight. I can see the "Bauhn" logo on boot which stays for about 5-6 seconds and then it disappears.

"No signal" can be seen moving across the screen. If I press the menu button on the side of the TV, it shows up.

So right now I'm currently at no sound and no backlight.

por

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