Ray
When you press in on the JV-2080's volume knob, you should hear a short audition phrase for the currently selected patch. Do you hear this? If not, then you need to turn up the volume, or the JV-2080 has internal audio problems, or there is something wrong between the JV-2080's audio outputs and your sound system. If so, plug in a set of phones and check again.
If the audio checks out ok, it is time to move on to MIDI. In the upper right corner of the front panel, the JV-2080 has a green "MIDI Message" LED that flashes when incoming MIDI messages are detected. Does this LED flash when you send MIDI messages to the JV-2080? If it does, but you hear no audio, then the JV-2080 probably has internal electrical problems or some kind of weird set up problem. If the MIDI Message LED does not flash, then the JV-2080 is not detecting any incoming MIDI messages. If you are running the JV-2080 in "Patch" mode, then the currently selected patch must be set to receive on the same MIDI channel that the source (keyboard, Sonar, etc) is transmitting on, or there is no communication. Likewise, if you are running the JV-2080 in "Performance" mode, at least one of the 16 "Parts" in the Performance must be set to receive on the same MIDI channel that the source is transmitting on. I apologize if I am being overly basic on this, but I have no idea of your expertise with MIDI devices, so I am trying to cover all the bases.
To answer your question about a 5-Pin-DIN MIDI port going bad - YES! The 5-Pin-DIN MIDI ports - both IN and OUT - are equipped with opto-isolator (opto-coupler) chips that electrically isolate the connected devices from one another and prevent the MIDI ground loop hums that plague this modern day USB-MIDI stuff. Those opto-isolators are extremely susceptible to static electricity damage. That is why it is not a good idea to drag one end of a 5-Pin-DIN cable across a carpet, during dry heat winter-time, with the other end still connected to a MIDI device.
Good luck with this ! Keep us posted on how things are going.
Regards,
Ted