check across the output fixed 1 n 2 with a ohm meter more then likely you'll se a dead short and usually caused by TVS diodes arcos all four channels. check across each channel red n black terminal, you will find at least one or 2 of the red and black outputs shorted! you can cut one end of the diode ounce you find the short. with one end disconnected actually go across the diode by itself see the short then l while disconnected. if you loose the short when shorted didoes is removed. then what you'll need to replace to put the tiu back in working order! the diodes are used for voltage spike protection from derailments and accidents!