I think the problem is not in the cable.
Though I am not using the same cable with you, I can tell you how I check the cable and board:
1. Cable check:
Connect 3.5mm to rs232, and rs232 to usb, and usb to my laptop. Now I can see a COM device appears on my laptop. (I don't connect the board right now because we just want to check the cable). Next, I use a small wire to short the RING and
2. Galileo function check: