Sprinklers
There is either debris in the diaphragm or you could have a bad diaphragm. You could also have a bad solenoid.
First, unscrew and rescrew solenoid, making sure it is not dirty underneath. If this fails to solve the issue, take the solenoid and put it on another valve. If this new valve's sprinklers start to leak, you will be able to tell that the solenoid is bad. You can also test the solenoid with an ohms test using a multimeter on your circuit board.
Checking solenoids and field wires
1) Set meter to OHMs
2) Set range to 200
3) Remove common wire!
4) Hold tip of black probe to common wire
5) Touch red probe to each station screw
**Short circuit/Bad solenoid/Wire=0-12 ohms
**12-60 ohms Good solenoid
**High numbers=corroded wire
**200+=Broken wire
If you find that the solenoid is good, then the problem is mechanical. Make sure your bleed screw and bleed lever (this will be a lever under the solenoid) are tightly closed. If they are closed, then the problem lies with the diaphragm or the valve itself. Take the valve apart and clean out the diaphragm and underneath inside the valve body. Reseat the diaphragm.
If this last step does not work, you either have a bad diaphragm or you could also have a crack in the valve. If it is an old valve, the plunger may have rust. In this case, you can try replacing the diaphragm first. If replacing the diaphragm does not solve the issue, it may be time to replace the valve.