Dear: The sources of these equipment are not very complex. They have the input circuit, a PFC circuit, the source that delivers the 12v voltage for the controller board and the 5v or 3.3v standby voltage and the on and off circuit. Some equipment has a separate source for the 12v voltage and the stand-by voltage and others incorporate the ballast that feeds the lamp on the same source plate. The first measure to be done is in the cable that goes from the source to the controller board. With the equipment connected to the network, the standby voltage (5v or 3.3v) should appear on one of the pins of this cable. If it does not appear, disconnect the controller board and take the measurement again to discard the board. If the next measure to be taken is still not present at the PFC circuit output, the rectified grid voltage should appear. If this does not happen, the next measure to be done is the rectifier bridge where the rectified grid voltage should also appear. Take precautions to work in these sources, since they are not isolated, so that when energized there is a possibility that the living phase is connected to the earth with the consequent risk of an electric shock. It is what is called "hot land." For your safety, use an insulating transformer to work with these sources. I hope it serves. Regards.