Inground sprinkler problem?

One of the zones in my sprinkler system will not work. When it is activated, none of the sprinklers raise. Instead, a puddle starts to appear near one of the sprinklers. I am assuming theres a cracked pipe underground around there, and that causes there to not be enough water pressure to raise the sprinklers (makes sense?). How do I go about replacing the cracked piece of pipe, assuming thats the problem? It is 3/4" black plastic tubing. Also, the sprinklers I have are Rain Bird 5000 series. Are they good heads? The gears are broken in one of them, so I will be replacing it soon. Should I keep with the 5000's or consider something else?