Hi,
The screen in the TV not showing the picture well, I think some cable might have become loose.
The TV screen is not showing the film properly. Perhaps, some problem in the TV channel provider.
The picture in the TV screen is not proper. I think some problem with the cable, may be the cable which comes from Channel provider loose.
We say these things idiomatically, thus -
The TV does not have a good picture. I think some cable might have (be)come loose.
The TV does not have good reception. Perhaps there is some problem with the signal. The idea is that your TV receives a signal from the TV station.
Best wishes, Clive