Every day we see this type of post regarding self television repair. This explains why you can't diagnose television problems on an online forum. The television sections are really only for help with manuals, wall mounts and remote codes.
Here are similar questions that we see often.
I've replaced everything in my television because it previously had a black screen with no lighting. Now it doesn't turn on at all and all I have is audio. What could be the cause ?
Turns on and sound works fine, but the picture is distorted (solarized? polarized? not sure what the term is) I replaced the main board, but that didn't fix it.
I have an LG 55LM6200-UE with a dim lower-left. I just replaced both LED strips with no resolution. There is no physical obstruction visible, so this has to be a cable or board problem, right?
So your television stops working properly and you think it must be easy to fix, because you can buy boards on eBay, and you can watch YouTube videos. So you make a decision, you buy a board and you fit it, but the television still doesn't work as it should! This is a classic case of the 'let's try replacing this' method of television repair and illustrates why it is a bad idea. It doesn't work for a number of reasons.
To correctly diagnose issues, you need to know every board, what it does and every component on the board and what they do. You need to know which part has failed, replace the failed component, or replace the board. The parts you purchased off eBay were probably out of scrapped sets and not tested. The part you put in was dead when you put it in, so you just moved on to another guess at what might be the cause and replace a board that is fine. And so it goes on, you change all the boards and it still doesn't work because your first replaced board was a dud. Did you notice the large print that says 'NO Refunds, NO Returns'. This is to stop you sending your old one back and saying it didn't work, but the unscrupulous sellers use it as an excuse to get money for selling items that may, or may not work! The course to be a television engineer is 2 years full time education, and they own thousands of dollars of test equipment. Take it to someone that knows how to diagnose and fix. It is by far the cheapest option. The part that failed might be a 20 cents fuse diode hard soldered to a board. They will charge you $5 in parts and a couple of hours labour. It's not the fix you want to hear, but it really is the best advice.
Andrew - Fixya Moderator - Expert