You need to select a fairly slow shutter speed otherwise you will get just a sampled horizontal section of the picture.
As stated above, do not use flash otherwise you will get reflections and probably wash out the tv picture image.
You need to experiment to get correct exposure of the cabinet whilst using a slow shutter speed. This may give rise to a rather overly bright tv picture image so you may need to reduce the brightness and contrast below normal viewing settings. Again, just experiment once you have got a good cabinet exposure.
HTH
Peter
