Do you have a digital multimeter?
OK, in the middle of the TV you have the control board, it's the small green board that connects everything together. On it there is an LED that will blink or not.
The X-main and Y-main are on the bottom and top of your image, respectively. They are orange/brown boards.
The grey connectors on them can be disconnected, they are the power connectors.
Power to the set must be disconnected. Unplug the X-main first, leave the white and orange connectors plugged in. See if the same thing happens, and note if the green LED on the control board changes behaviour.
Disconnect power to set again then try with Y-main unplugged (X-main can be left disconnected.)
At this point, you really need a meter to make more tests.