To enter the Range Check mode, hold S4 while turning on the transmitter. The is the far right-hand button that's below the touch screen. The transmitter will then display a screen that says, "Transmit?" Press "NO". Then go into the System Menu and then the Range Check function. It will ask you if you wish to perform a range check. If you do, press the "Yes". The transmitter will be in a power-down mode for 90 seconds and the display shows the countdown. If you need more time, just press "Restart". If you're done, press "Exit" or just let the time run out. Return to the main screen in the normal manner. The transmitter will be back at full power.