Have you tried
tilting the LCD and see if the symptom change?
If tilting the LCD shows good video, then you have a loose or bad LCD cable going to the System board.
If tilting the LCD does not change the symptoms,then it is the "Inverter" board.
The laptop have an "Inverter" board that goes out and causes this problem. It is located just below the screen on most laptops. I usually purchase
them from here:
You may have to copy and paste this link into your browser.
If I could be of further assistance, let me know. If this helps or solves the issue, please rate it.
I’m happy to assist further over the phone at https://www.6ya.com/expert/joe_8b8c2cd6ce148309