It is right down the middle of the top of the wood that is the top flat piece that is also the desk top on my Day Dreamer. The TV is also located their but it is attached to the wall and not on the wood itself.
Is the wood directly exposed to the heat from the fire place? is it getting hot? If so the problem is that the heat is drying out the wood causing it shink and crack Just like seasoned fire wood. Pictures would be nice to see the location. Depending on how bad it is replacement mybe in order and then install a heat deflector or vent the area. The lack of or too much humidity plays a big part in how wood reacts and of course the quality of the wood is a factor.