With cable C disconnected, there is no power draw at all since there is no power being sent to the board. The problem is likely to be a shorted transistor on the output side. There are 4 in this unit. They are the 3-legged parts connected to the heat sink. If you have a meter that has a diode check mode, test the 3 leads of each transistor. They should read around 0.6 with a diode checker. If they read shorted , then they are the problem. Note: There are likely to be other parts that require replacement as well as the transistors.
Dan