Do electronics companies publish the diagram of their electric boards
If the manufacturer provides a service manual, it would be there. In the very old days it was common to have the schematics inside the manual or sometimes even glued to the inside of the case on old television sets, but those days are long gone. For test and lab equipment sometimes the schematics are provided with the detailed user manual. 

Most consumer products are very reliable and not easy to fix so it makes little sense to make schematics available to to the public. 

Sometimes 3rd parties like Sam's will provide service manuals. 

Even without service manuals, looking for power supply problems and obvious connections between subsystems, backlight inverters and so on can allow a substantial subset of common issues to be repaired.