A method and apparatus of testing a computer having a controller includes adjusting a reference voltage signal from a first level to a second level in response to an output from the controller. The first level is a level of the reference voltage signal during normal operation of the computer. Operation of a receiver in the computer is tested with the reference voltage signal set at the second level. An input of the receiver is connected to the reference voltage signal. Next, the reference voltage signal is adjusted back from the second level to the first level to enable normal operation of the computer.