Limit Switch X/Z not Working

Hello All,

I recently purchased a D 840 but from my first run I noticed that Z and X Limit switches are not working. The machine bumps on it and do not stop.
From the Diagnostic page in UCCNC there is no response from the switches while when I'm trying with the Y switches it works perfectly (I12 Green, XYZ Home/limits all Green).

For test: I've tried to connect the Z/X switches to the Y1 and Y2 board sockets and they both works, so the switches are not broken.
Second test: I've tried to connect both Y1 and X cables in the same Y1 socket but it does not work (no response in the software), I guess they both need to be clicked at the same time to work because they are "Normally Closed" switches.

After this I'm starting to think that the problem are the connectors on Motherboard or the motherboard itself.
Any suggestion on further tests? Or should I just replace the motherboard?
Thank you.