Panasonic TC-L46E50 comes on,full screen 10 sec goes off red led constant blink.

I am constantly amazed the money and effort put into trying to repair anything, that you know nothing about. Fixya needs to vette ridiculous questions.

Here is a video on this.

Sounds like LED lamps in the panel to me

1. Hold the front panel power button for over 15~20 sec and try.

2. See the youtube video
https://www.youtube.com/watch?v=awnrE3k_G2M

First thing, check the HDMI input and make sure it is firmly connected, same for the power cable, obviously. My Samsung goes similarly nuts if it detects no signal from the currently selected input but after 1-2 minutes it eventually stops and I can change the input source.

Before going OFF, the standby LED might blink. These blinks are fault indication. The number of blink should be counted. Count the number of blinks at one time, before the TV goes OFF. [eg: 4 blinks Power SOS P Board; 6 blinks Driver SOS 1 SU / SD / SC Boards
(SC energy recovery circuit)] and so on. you can get more details from this site named 'Electro-help'. You can reach it by searching the keyword "electronicshelponline" by internet.

the picture comes for 2 secs on the screen and immediately goes to stand by and red LED Sony bravia standby mode blinks 8 times

Flashing RED lights in Panasonic TVs means a fatal error code. Unplug the TV, wait 1 minute and replug. If the LED still flashes it needs professional service.