the starting electrolytic capacitor is probably fried. You can tell by its puffed out appearance when it is supposed to be flat. The thing that looks like a battery solder on. or also could be white and plastic but all cylindrical.
I am not an expert in such things and I know little about tv but I just wanted to plant an idea - the screen of a modern tv is dark unless there is something to be displayed, either a received signal or something generated by an internal menu.
Presumably there is a relationship between the output from the part of the circuit that receives and processes the signals and the brightness of the screen.
Perhaps that relationship is proportional so a reduced output from the signal part results in reduced brilliance?
Many people replace circuit boards and hope but if you want to find and cure the fault I think you will need a couple of years experience, some test gear and access to a technical library.
Obtaining a service sheet and checking a few voltage would be a start but in reality I think making friends with a local repairer would be favourite, especially where the in-laws are involved...
These blinks [flashes] are fault indication (Error Codes). From the number of blinks occur at one time switch ON, you can get an idea about the faulty circuit section inside it. This will make repair easy. These are called blinking codes. Make sure about the exact number of blinking of the standby/power LED, by switching On & OFF the set, for at least two times. Count it carefully. If you wish to get some details, check the site linked here. It has details about blinking codes, and fault locating procedure, to many popular brand TVs and other devices. http://electronicshelponline.blogspot.com/https://homenol.blogspot.com/https://elektrotricks.blogspot.com/
Blinking codes details to many popular brand TVs are given. If blinks continue without any pause, the main board is faulty.
Hello Sir 6x is stand for back light please check backlight with backlight tester if ok then check power supply in this case set is old like 7year and confirm back light is defective replace the back light