  We explore the overlap of two nationally-recognized learning outcomes for
physics lab courses, namely, the ability to model experimental systems and the
ability to troubleshoot a malfunctioning apparatus. Modeling and
troubleshooting are both nonlinear, recursive processes that involve using
models to inform revisions to an apparatus. To probe the overlap of modeling
and troubleshooting, we collected audiovisual data from think-aloud activities
in which eight pairs of students from two institutions attempted to diagnose
and repair a malfunctioning electrical circuit. We characterize the cognitive
tasks and model-based reasoning that students employed during this activity. In
doing so, we demonstrate that troubleshooting engages students in the core
scientific practice of modeling.
