The four HDMI ports are dead on the TV, for no reason, overnight. This is usually due to the HDMI switch chip on the motherboard of the TV that is dead because it has overheated, or the welds have oxidized or there is too much dust on them, or it is still in good condition but the programmed obsolescence is doing its work. The last cause is most likely, especially if the TV is less than 6-7 years old and you do not use it that much.
What solutions are available to us?
First test the easy solutions, and finish by the hardcore ones. In parenthesis: the number of people that tried and the success rate.
1. Try different HDMI cables (success rate 0% [0/5]).
2. Unplug TV energy for 15-20 minutes (success rate 66% [4/6]).
3. Unplug both TV and external device power for 15-20 minutes (success rate 50% [1/2]).
> If you change the HDMI cables while the power is on any of the items, then it can deliberately corrupts the code / signal between the devices. The disconnection will reset video signal caching.
4. Plug the power to another source (> not enough power) (success rate 100% [2/2]).
5. Retry auto tuning (success rate 100% [1/1]).
6. Change inputs labels (sources labelling, source > blue button) (success rate 50% [1/2]).
7. Firmware upgrade (Connect the TV to the Internet box, menu > red button > check updates) (success rate 0% [0/6]).
> You can try firmware downgrade, although it is a much more complicated task.
8. Reset TV settings (Factory reset in parameters > options > factory reset) : (success rate 66% [4/6]).
9. Set the correct settings 1080i, 1080p, color depts, scaling : (success rate 100% [1/1]).
10. Buy a new motherboard : 115 dollars (success rate 80% [4/5]).
11. Repair the motherboard : 200 dollars (success rate 100% [6/6]).
12. Make a scandal with LG support even if the warranty is over for a very long time to make them repair the motherboard (success rate 100% [1/1]).
13. Buy a HDMI to VGA converter (1080p quality) (success rate 100% [3/3]).
14. Buy a HDMI to YPbPr converter (1080p quality) (success rate 100% [3/3]).
15. Use an industrial hair dryer above the HDMI processor ship at a small distance for about 40-50 sec (success rate 68% [36/53], with 2 very bad cases where the TV was totally dead at the end). Test at your own risk.
> the bumps of solder of the main processor are brittle because of extreme temperature exposition. The TV should have a space of 10-12 inches with the wall to let the air cool down.
16. Baking the TV motherboard (put on a cardboard, face up) inside an oven (not the microwave as there is metal parts) at 396°F for 10 minutes (success rate 91% [68/75], with 3 very bad cases where the TV was totally dead at the end). Test at your own risk.
> The idea is that there is a crack in the solders, baking the motherboard will melt the solders again. It is advised to remove the plastic parts as much as possible, especially the audio IN RGB plastic part. There will be a terrible smell during the cooking. Take a picture of the motherboard and its connections before disassembling it to see how to put it back at the end of the processus.
17. Replace the HDMI switch chip, TDA19997HL/C1 (very complicated, you have to know how to weld, success rate 100% [2/2]).
18. Attach a 20x20x10 mm heat sink to the chip after baking. You will have to cut the back plate (success rate 100% [3/3].
Hair dryer and baking
Solutions 15 and 16 are very hardcore. It is better to try them when the TV is completely dead (no power) even if the baking has a good success rate. Also, these methods may only last few months, few weeks, few days or even few minutes. Maximum 2-3 months for the hair dryer and 7-8 months for the baking one. If it doesn’t work you can test two more times, each time you will have to let the motherboard to cool down for at least 30 minutes.
The best solution
The most reasonable solution and the most permanent one is to employ a converter between the HDMI and one of the other ports of your TV (solutions 13 and 14). These ports don’t have a switch processor, so the issue is not likely to repeat again with them.