I have a dead battery/ac powered radio that I'd like to use to learn how to repair things. But I'm already stumped. There's a component near where the power comes in that I can't identify. I'd like to test it because there was some rust and dirt near it so I suspect water damage. There are no markings on the component. Is there anything I can do to identify it then test it? It's the black thing in the middle of the picture. (And if this isn't the right place to ask, please suggest where would be better.) EDIT: I forgot to say it has 3 pins. I'll try some of the advice below.