controller 2 crashes the game/console

[vectormz]

I've built 3 NES so far using Open Tendo boards, they work great (i love this project)! but they all have the same problem: whenever controller 2 is plugged in, makes the console crash, sometimes scrambles the image, or if they're both plugged in and i start the game i can't get past the menu, i tried soldering new controller board connectors, different controller, swapping ports, new ports cleaning ports, inspecting the board for solder blobs... and nothing.

NOTE:
when using only controller 1, everything works great, games boot up every time, sound, buttons are responsive, everything works.
I really don't know what might be the cause, or where should i start diagnosing ( i like to solder console stuff but not savvy when it comes to measure values of components)

Any help would be appreciated,
Thank you.