Step 1:- Press the TV Home button, if the TV menu is not showing properly then TV needs repair, else follow the further steps.
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Step 2:- Disconnect the HDMI cable & connect it to an alternate port(if available). Plug the device back in, and change the TV to the new source to see if the issue is resolved.
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Step 3:- Restart your TV & external device to see if the black section is still appears on the TV screen. It is does, your TV needs a repair.