One way, get a meter with milliohm accuracy, like 1.000 ohms, then put the ground lead on big ground planes and move red lead along the plus path, the lowest resistance is most likely where the short is. Other way, use a high current supply, set to correct voltage, current limit off then connect power source to circuit, (Do this after the regulator, Your using power supply ) if your lucky, the short will produce smoke and there is your bad part. Note: last method can burn traces if short can handle more current than your traces.