Hi,
Here’s the [https://elektrotanya.com/panasonic_tx-42as650b_tx-42as650e_chassis_la51.pdf/download.html|service manual] for the TV. (be patient as it takes a little while to go from ''processing'' to ''download'' once you have checked the “I’m not a robot” check box and clicked on Go to download, under the Document preview box).
In the manual on p.19 Sect.7.3 you’ll find the LCD panel test mode procedure which may be a good first step. Looking above at Sect.7.2 it shows that a single blink may be either a faulty panel or the P board.
If the panel appears to be OK then on p.32 there are the voltages and test points for the P board and the A board that can be checked.
The manual also has full schematics, assembly instructions and a parts list
Hopefully a start