I have connected the power supply to the master to check the cabling.
First I had to setup a cable to take 5V power and then I set up a flat 40 pins cable to test J3 and J4 connectors.
Hard disk flat cables have one pin closed, if I recall well it is number 10. However it can be successfully opened with the dremel. I have then grouped the 40 cables 10 by 10 and marked in black the four grounds.
I am now sure that the power supply and the USB cabling is well done and ready to be used.