StreamSmart 400, missing wire

[inakiz]

Hi.
I have opened a StreamSmart 400 to see what is inside. To my surprise one of the cables coming in from the "serial" cable is not connected to anything. There are four cables: green, white, red and black. The former three have a labeled position in the board (G,W,R) but the black one is floating around. Probably it was soldered to some part, but I cannot find a clear pad where it should be soldered.
Please, anyone having this device would take a look where the black cable is connected?. :-)

Inakiz.