This paper demonstrates the capability of MODEL-ECS to support domain users in rapid prototyping of executable problem solving methods (PSMs) (i.e., known as inference structures in the KADS models of expertise). MODEL-ECS is a graphically based conceptual modeling language that is made up of Conceptual Graphs [14] and Actors [6]. In addition to being highly formal and considerably sophisticated, the PSMs resulting from modeling using MODEL-ECS is executable (i.e., executable prototypes). This enables the knowledge engineer to immediately test, and if necessary re-design his knowledge model. This is a major advantage to the contemporary approach of performing the modeling process, and then carrying out the prototyping activity (where one builds a prototype knowledge based system). This paper attempts to demonstrate the capabilities of MODEL-ECS by modeling a simple PSM for Audio System Diagnosis.