Famicom AV controller port not working

[stompkatz]

Hi, this is my first post in this community. I have read here for a while but today I'm seeking for help with a particular issue it just happened to my Famicom AV. I was about to install a NESRGB kit and I removed the PPU, installed the socket and place the PPU on it to check. The video and audio are working fine, but the controllers do not respond. I have checked the controllers working in another system so I guess this issue is related to the Famicom ports. Does anyone know what are the common issue with this specific part of the console and how to test/repair? Thanks in advance!