The Corbin Russwin ED6200, 736 or 3700 latch bolt not extending is usually caused by one of two problems.  One of the problems is the crossbar screws, tenion sub assy, and crossbar are not tight.  The Corbin Russwin ED6200, 736 or 3700 does not have a heavy spring on the active side case, it is on the inactive side, and if it is not tight the crossbar will move from a non parallel position to the door.  This can be corrected by tightening the crossbar screws, but sometimes you have to shim the tenion sub assembly.   The only problem might be the springs or the active housing.   I would try the Crossbar screws first.