iMac A1419 screen ficker

[MaxFix]

Hi,

I have an iMac 27-inch from Late 2013 with flickering screen issue (exactly as on the video from the link). Tested with another screen and LCD cable still flickering but differently (the whole screen flickers ON/OFF with another screen).
What do you think it can be?

THanks!

 

[2informaticos]

It looks like screen issue.
On external screen flickers the same down area?