Now we're getting somewhere.
To make sure the outputs are OFF, you should:
a) connect a 10k pull-up resistor to the "G"-pin of the chip
If you want all outputs to be "active" (represent the data you shifted in), pull this pin LOW. If you need all outputs to be OFF, pull it HIGH.
b) use the "CLR"-pin to reset the chip to OFF whenever you need it.
You're the best !
Now it works like it should !
I put a resistor between +5V and the IC_PIN_8 (G), then connected the IC_PIN_8 to a D_PIN of my arduino.
When the module starts, it nows puts +5V on the IC_PIN_8 (G) which puts all outputs to no drain.
Then in my arduino's setup, i have a byte sent which puts all outputs to OFF and release the G pin to LOW level.
After this, i never touch the G pin level anymore as it only deserves what i wanted to have : ALL OUTPUTS OFF AT START
In fact, when i read the datasheet, i thought that the G pin was the solution, ...... but !
As i'm really not as good as i would like to be in electronics, here is where it droves me
Thank you for your precious help !
I greatly appreciate !