An electro-mechanical position servo is introduced as a benchmark for mode-based Fault Detection and Identification (FDI). The purpose is to provide a simple, industrial system as a platform for comparison of model-based FDI methods, and for the gathering of design experience. Despite a simple system structure, FDI design is intricate when realistic obstacles are included: unknown load torque, unmodelled dynamics, elements with saturation and backlash, and measurement noise. FDI performance specifications are provided. They include requirements for detection probability and time to detect. Two mathematical models are given: a simple model for use during design, and a complex, nonlinear one for simulation and verification.