Sorry if i didn't response .... I'm french and i don't unsterstand all the answsers
My Multimeter is a pro so i guess the value is correct !
When I tried to mesure the voltage, I take 2 mesures
1 at the points of the led strip => 4,71
The other was at the points of the raspberry without led strip connected.
I have just made this test:
RPI power with a usb charger
Led strip power by PSU with the grnd link to the raspberry gnd pin.
Same result: I have the rainbow but leds blink again....
Sorry, my case seems to be unsolvable....
Don't you think my led strip is damaged ?