Each year on my nice lawn after two hot days two spot about 6 feet appear and the grass turns brown. one area

Question:leads to a utility box the other about 30 feet away does not. i was told that the line going to the box may have rocks material covering the line underneath the grass and the rocks get hot and destroy the grass. how can i find out the cause and resolve the problem

Answers:
It well could be what ever is in the ground is a part of the problem.

It would seem that the soil or maybe rocks don't hold the moisture as well in that area.

You could dig it out & replace it with new soil, Because you know where the spots are you could water it more,

Or may be you can top dress (spread & rake it in) some peat moss in to the area.
You may not get enough in one try, because you don't want to cover the grass completely. The peat moss will help hold moisture.