This should be tested using a variable DC power supply, connected as displayed in the image below:

Once connected, begin at 0VDC and slowly increase voltage until the servo begins to respond.  That will be your "start-up voltage."

DFC90 Servo Start Up Voltages

Roll Servo should be less than 3VDC

Pitch Servo should be less than 3VDC

Pitch Trim Motor should be less than 5VDC