Ebox3350 Secret COM 2
The bottom part, showing the solder pads for the second COMM port.
Also note the Solder pads for ICs to the left of the COMM connector.
These solder pads need to be populated with a MAX chip or some protection as they bridge the processor pins to the COMM connectors.
With these unpopulated, the solder pads on the COMM ports have no signal.