Can you do a loopback on the serial lines? Connect RX and TX together with a jumper cable. These is physical pins 8 & 10. And then run minicom. When you type, you should see the characters in minicom. If they dont appear, it means serial is working correctly.
Install minicom; sudo apt-get install minicom
Start minicom; minicom -b 9600 -o -D /dev/serial0
You may need to kill gpsd first; sudo killall gpsd
Mark --OzzMaker.com --
PiScreen - 3.5" TFT for the Rasspberry Pi