Dreamcast controller auto disconnect

Hi there, I got a second Dreamcast, and the controller (only port 1) is disconnecting all time. I replaced the pico fuse F1, the resistor and nothing. I swapped the controller board with another working dreamcast and the problem kept happening. I also swapped the power board and nothing. So the problem must be in the main board. Any tips I should try? I also tried to direct connect the flat cable pins 3 and 4 directly on the controller board, to make sure it wasn't the flat slot (or the cable). the board is a VA1 one. Thanks for any help