Went out yesterday to take care of a 1-1/2" valve that wasn't firing. Went through the whole troubleshooting gig and then finally removed the bonnet and diaphragm assembly. Discovered that the nut/washer that holds the assembly together had broken off and that's why the valve was bad. Found the washer in the outlet cavity of the valve but couldn't find the nut anywhere. Decided to replace the whole valve since it was an older series and installed a completely new one. Fired it up and it wouldn't fully shut down, making an audible hissing sound. Took it apart and discovered a small rock wedged between the diapgragm seat rubber and the washer. Took it out and there was a visible indentation in the rubber from the rock. Decided to remove the valve and blow out the main line. After doing that and replacing the diaphragm assembly we finally got the dang thing to work. Then we only had four broken sprinklers and several clogged nozzles in the zone to replace. Pics of the diaphragm problems.