Analog circuits are often specified using non-linear equations, which are difficult to analyze. Therefore, test generation and diagnosis are problematic issues in practice. In this paper we propose a new method for diagnosis of analog circuits that uses combined information from tests at different frequencies. By solving simultaneously the resulting equations (one for each test frequency), we get a reliable method that decreases the number of possible answers to the diagnosis problem. The min-max optimization algorithm that we implemented for non-linear transfer functions gives good average runtime for diagnosis parametric faults.