Controller Port not recognizing controllers - Solved

I regularly purchase and repair playstation 2 fat consoles. This particular one, a 30001 R model will not recognize controllers in either port 1 or port 2. Ive used several controllers that Ive previously tested as functional. I then replaced the actual controller port itself and achieved the same result. I replaced it a second time with another controller port with no change. I thought that it must be the ribbon cable so I tried 3 additional cables that I inspected and were not damaged. Again no resolution. The only thought I have at this point is that the issue may be motherboard related, but Ive not seen that before and after an hour of scouring the web I still cant find an answer. Id appreciate any insight you may have on this issue.

Thanks!

Updated: 3/26/2015

After sleeping on it for a few days I decided that the only thing it could be was motherboard related. I had a spare available so I took apart the unit and swapped out just the motherboard. It worked excellent and the situation was resolved. Im not sure what specifically this issue is with the motherboard such as a blown fuse or short somewhere, but at least I have a fully functioning PS2. If anyone ever reads this and has any input, feel free!