Question
..I checked the URL below from my end and it worked.
..Its to a picture of the control valve I'm asking about.
I have a constant trickle from one of the sprinkler heads.
Which of the adjustment points on the control valve will stop this trickle?
..See pic at:  http://www.webphotos.com/view_photo.asp?mi=3&smi=2&a=85116&p=2778485

Answer
Mike.
 I really did try to go  to that sight but couldnt get it up. Any way there is no adjustment to keep it from weeping water. The valve is fouled or defective. If it is new it probably just has debri in it . If is old it may have just worn out. Turn the water off. Take it apart. Usually phillips screws, sometimes bolts hold it together. Get ready for possible drainage as soon as you break it apart. Try very hard not to get debri in the valve/piping. You may want to just barely break it apart and wait until it stops draining. It may not drain at all, depending on elevation.
Take all the plastic and rubber parts out. Look for rocks or something in the valve. They may have floated out when it drained. Look closely at the rubber part for tears, dents, or signs of dry-rot. Look closely at the plastic parts for cracks. The solenoid (the thing with the wires) plunger is especially suspect when a valve is weeping. If you think the valve is defective or worn take all the parts to your local sprinkler supply and ask for a whole new valve. This is going to be easier than buying a single part. Take that valve back home and disassemble it and replace the guts  in the old valve.
  Let me know if you keep having problems,
                     Thanks, Jim