Toshiba Model: 50L711U18 - Back Light is turning off after 10-15 mins

I have problem with my Toshiba Model: 50L711U18. The back light turns off after 10-15 minutes. I tried to restart it but the back light doesn't turn on. I used flash light to check the video, and video is still there. I unplugged my TV for about 15-30 minutes then plugged it again, the back light Turned ON, but after 10 - 15 minutes it Turned OFF again.

It seems like i need to cool down or let the capacitors to be discharged first before plugging back again.

I already replaced the power supply , thinking that this is the caused of the problem. But, it didn't changed anything!! The problem is still there.

Any suggestions Please...

Thanks