I have sound but a blackscreen

@henkdachief the principle for all these repairs is the same. Like you already figured out, you most likely have a failed backlight strip. Now to get to it, you will have to disassemble your LCD panel. Take a look at something like this video to see how it gets done.

Your Tv may look slightly different etc, but the principle is the same. If you are stuck with anything during your repair, you can always post some pictures of the area of concern. We can then try and help you out further.

在已经存在的问题里加入图片

While you work on your TV, take lots of pictures. Once you are done with it, take those pictures and create a guide for iFixit. That will help the next person that has the same problem as you do. It's easy and fun to create these guides. https://ifixit.com/Guide/new The iFixit community will appreciate this.