A testing apparatus to establish a fault by a process of elimination includes an input unit, a signal converting unit, a switch unit, and a display unit. The input unit receives an input signal and outputs a switch signal. The signal converting unit receives the switch signal and outputs a control signal. The switch unit receives the control signal and outputs a test signal. The display unit receives the test signal and runs a built in self test (BIST) program to test the proper functioning of the display unit. The signal converting unit outputs a data signal and a clock signal to the display unit when the display unit works normally. The signal converting unit not output the data signal and the clock signal to the display unit when the input signal and resulting control signal are repeated.