Hello there,

i have seen this problem before the Screen is going out and needs to be repaired .

but if you want to try and fix it here are some steps to try

Check all the connections if using HDMI try using a the AV cables .

Remove the power to the TV from the plug give it a few and power it back on if the black blotch is still there you are going to need it repaired .

i hope this was helpful don't forget to rate