Try the usual. Unplug it and all connections (I mean ALL!) wait a few minutes then apply AC then one HDMI connection.
Good luck.
Bob
New LG 55LM6400 began to blink after software upgrade. At regular intervals, approximately every 18 seconds, the screen blinks to black for a second - then back to picture - then black again - then to normal picture for about 18 seconds. LG support had no record of this problem. Has anyone experienced this or have any ideas for a fix. Attempting to upgrade software again was unsuccessful as software upgrade screen shows no wi fi connection, even though the Network Status shows connection. And of course tried the reboot basic(unplugged/replugged TV from power source)..

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