Desoldering a chopper transistor

As you are just trying to isolate the device for testing, sometimes it is easier to open the circuits elsewhere to achieve the isolation. For example, if the collector goes to an offboard transformer through a connector, then that lead is easily isolated; the base is probably fed by a resistor and lifting one lead of the resistor will isolate the base. With 2 of the 3 connections to the transistor open, it is isolated for testing purposes. TO-220 packages (3 leads with tab) can be very difficult to remove in one piece when - as Pete was mentioning - the holes are to small. Some manufacturers fail to increase the drill size for the wider TO-220 pins, they can be very tight with no room to wiggle the lead to break the final solder bridge. Sometimes slightly twisting the lead might do it. Sometimes you have to rock the device up and out of the holes with several heating cycles.