One sector in irrigation system does not work?

I've got a Rainbird sprinkler with 3 sectors. One sector waters the front yard and 2 sectors water the back yard. I mistakenly umed that the irrigation system was not working and fiddled with the controls on the flow valve in the back yard. Turns out that the problem was simply that the water was turned off. Now with the water turned on, the front yard waters just fine. But only on of the two sectors in the back yard work. I cant tell if this is a result of my having played around with the flow controls or whether there is a thrid flow control valve that needs to be turned on. Is it common to have the water flow to two sectors go through the same valve or should there be a third flow control that I need to find and turn on?