@Poblofre
Before you send in for repair, try the known fix for the flashing screen on TCL RokuTVs first. (Common backlight issue on older LED TCLs), so lower Brightness to Normal)
1. Start up a show either in antenna or using Roku.
2. Press *button on Roku remote. An Options screen should appear and you should see "TV brightness". Change this to Normal. Apparently some can use "Bright", but run into issues when using "Brighter".
3. Press *button again to exit.
This may work for you and stop the flashing. Not really a full fix since you can't use the full array of brightness options, but if does resolve issue, then at least you know it is a backlight issue. (You can normally see it flashing/blinking from the back of the screen through the back cover).
Apparently, bad design with LED driver and current/resistance regulation and an undersized heat sink. Replacing power supply board ($20-50) will fix your issue because contains power supply but chance may just reoccur some time down the road. If the fix mentioned above works for you, I would use TV until it dies. (The lower brightness level is using less current). If it does not, I would simply look for another TV. Unless you know a really cheap TV repairman or replace the power supply board yourself. (disconnect power, wear gloves, and don't touch the old capacitors on old board, or at least discharge them first.)
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102
