If the concentrator displays AC, but there is no activity on any of the ports, the most common cause is a node number setting. The way to check this is to turn the unit off and back on, when it displays P1 press the right pointing arrow key. If the number is incorrect change it by pressing the left arrow key, untill it displays the correct number. Press the right arrow key again and that will save it. The c/cons must be numbered sequentially starting at 1 from the host out, and can not skip a number. If you are using an AIX system the opposite arrow keys are pressed.