NUON Samgsung Extiva DVD N2000 - 2nd controller port unresposnive.

Recently I finally took the plunge and bought a NUON, hoping to one day be able to experience Tempest 3000. While the unit works great otherwise, whenever I plug in a 2nd controller it'll recognize its existence but won't respond to any button pushing. I've tried using both an HPI Warrior and Stealth, both known working controllers, to no avail. Any ideas?

 

Normally unresponsive controller ports are down to fuses i think