Peek down the hinge when the device is open. You can clearly see two ribbon cables. Since the mainboard is behind the screen, I would assume that one cable is for the battery & one is for the keyboard & sockets. That's just a guess tho.
The cables don't appear to be under any stress when open, so hopefully Psion 5 cable issues won't be a problem. Although, I never had any issues with mine. I broke the screen once (by standing on it) but that's a different matter.