Peter gave me the hint that the default values are stored in an eeprom in the laser head. So connecting the head to a driver not used before shows the default values for the head. For this head it's 0.86A. So i measured the slope of the NPRO up to that value, reaching the 100mW at the default value stored in the head without tuning the diode temperature. So the head seems to be refurbished and not dead...