Original post by: Markus2 ,
try factory reset to avoid any software bugs. If still same problem may be some bulge or broken capacitor (usual after some years). see [guide|4131] or look in google images/youtube for replace failed capacitors. Now open TV and see if you can see any leaks (like dark liquid). In ifixit forums also there are tons of people fixing by soldering. Open TV and add picture to this post.