Question
Our Rainbird sprinkler system has 6 zones, two in the frontyard and 4 in the backyard.  Currently we only want to use the backyard sprinklers but the 1st zone in front yard turns on during the last water cycle and does not turn off until manually turned off.  Is this caused by the 100dv controller valve?  If so can I simply replace the diaphragm I believe this includes the solenoid or do I need to replace the entire controller?  If it is not the controller then what is the correct problem?

Answer
Thanks for the question.
Well it sound as if the control valve is the problem. The simplest way is to replace the entire top of the valve which includes the solenoid and diaphragm. The diaphragm is a rubber piece that is just under the top. You will need to replace that separately, since it is not attached to the top part.
PS Buy an entire valve, it's cheaper than the 2 part separately.
Good luck.

Matt