Totally agree you need to first know, what variety/s of grass are you talking about ??
Then tell us how high or low have you been cutting it ?? Needs to be highest in the hottest weather - unless its a Bentgrass which is what they use for golf course greens...
And get your sprinkler timer working correctly, turn it on so you can see if each zones sprinklers are all coming up and are not turned the wrong way, plugged up, broken, etc...
Some varieties get fusarium blight, and other stuff, some get nothing..
Some get attacked by lawn moth grubs, june bug grubs, and stuff like that, leaving brown patches...
Some grass is full of dead grass at the soil level that creates a thatch, making it harder for food, water, and sun to get down there and do their jobs..
All grass will benefit from yearly de-thatching if it has it, and a good aerating which will pull little plugs out of the lawn soil and deposit them on top..
This will now allow air, food and water to get down to the root systems quicker and more efficiently...
Leave the plugs on the top of the lawn so they can break down and help exchange the top of the soil with the soil underneath..
Ever wonder why golf courses fairways and especially the greens look so good ??
Because they dethatch, aerate, feed, water, and cut the greens every morning in 2 directions...
And they test the soil to determine exactly what it needs in terms of PH level and food, and any trace elements it might also need...
Dan F