Have just got a Hitchi 4K TV 65U6763DB Ultra HD which has 4x HDMI 2.0 ports.
Have tried the Fire Stick in all HDMI ports, but all have the same bad picture quality. Picture breaking up and dull un crisp picture quality.
How can I sort this please?
Try checking your Network Status. From the Fire TV menu, select Settings > Network, then press Play/Pause on your remote. The Network tool will check your connection and if there are problems, it will display some troubleshooting steps.
There are also some additional 4K Ultra HD TV troubleshooting steps you can try - Read more about checking your settings here and read more about compatibility and system requirements here.
If following these steps does not resolve your problem, let us know what you've tried and we'll see what other suggestions the community has to offer!