Be sure you check the setting that in some you may have reduced the display brightness. If so, a quick fix, adjust it. Otherwise if not the problem then more than likely some true h/w issue is at fault. Since, you described a "backlight" PCB is weak or faltered. You need to teardown and replace the part provided you're capable. Of couse, you can have the tech repair service do this at some cost which is a major fix but overall can be easily gotten to depending on your model laptop. You should check by goggling what is required to do and "YES" similar laptops should provide a guide or YouTube instructions if you go that route once you locate and get the right part. Alas, it appears to be working though weakly, it may have a broken solder lead, a quick reheat and flow of solder can fix that if the source of the problem. I hope this helps.

Oh yes, it always helps to provide what model# you have, we're not mind readers.

tada -----Willy Happy