I had a problem on a similar model. The mainboard needed a solder reflow, specifically, the XD CPU chip under the big heatsink. I wrote up the process in detail at https://lab.remaker.com/2020/11/lg-47lw5600-power-light-blinks-red-3.html, but it’s the same as any BGA reflow: Remove the heatsink to expose the troublesome chip, optionally add flux, shield the surrounding area with foil, heat the bottom, and use an oven reflow of your choice.
I used a cheap heatgun, with the 550 F setting (low), heating the underside of the board for a little over a minute, and then heating the top side for four minutes, with the heatgun always moving in small circles.
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You can also take the board to a repair shop to get the chip professionally removed and re-balled. eBay has a number of services that will do this by mail.
I had a problem on a similar model. The mainboard needed a solder reflow, specifically, the XD CPU chip under the big heatsink. I wrote up the process in detail at https://lab.remaker.com/2020/11/lg-47lw5600-power-light-blinks-red-3.html, but it’s the same as any BGA reflow: Remove the heatsink to expose the troublesome chip, optionally add flux, shield the surrounding area with foil, heat the bottom, and use an oven reflow of your choice.
I used a cheap heatgun, with the 550 F setting (low), heating the underside of the board for a little over a minute, and then heating the top side for four minutes, with the heatgun always moving in small circles.