[Q] [HELP]not able to go to Download mode ,Samsung galaxy s duos s7562 topic

Hi ,
please help me im not able to enter into the download mode of my samsung galaxy s duos s7562
I press the vol.down+home+power button, but then the yellow triangle just flashes on the screen for some miliseconds and then the device starts vibrating(i still keep holding the buttons) and after i relase the button it starts normal booting.
PLEASE HELP!!