This report describes the Generalized Maintenance Trainer-Simulator (GMTS), an instructional system designed to give electronics students intensive troubleshooting practice in a simulated hands-on training environment, and reports on a field evaluation of the GMTS applied to systems level troubleshooting in radio communications. The GMTS can be used for any device in which signal paths and their relationships to controls, indicators, and test points can be defined. It generates interaction with the student by referring to his last inputs and to its stored history of interactions with him up to that point. To the extent that these individual student histories constitute models of individual students, GMTS constructs a model of each student to interact with that student. The computer program that implements the instructional system is indifferent to the specific equipment being taught, since specific equipment for simulation is determined by loading two bases for that equipment describing its essential features. Results of field evaluation of twenty students who practiced solving 35 troubleshooting problems were: (1) more uniform fluency at troubleshooting; (2) decrease in mean times to solve a problem; and (3) a more favorable attitude toward the trainer. (Author/CWM)