The r3R3 uses a atmega16u2an ATmega16u2 in place of the ftdiFTDI. It is possible that it is not loaded, busted crystal, or it has no local power to it. Where itIt is a small smtSMT.
You could use your good arduinoArduino setup as icsp progammerICSP programmer to talk to the icspICSP of the 16u2. To to see it is alive. And if so then program it.