I don't have a revision number for the Sparkfun shield - it is marked 5-17-11 underneath though.
I believe it was originally hand assembled (looking at the solder), but I inherited it for my honours project.
I had my suspicions about the power draw on the N+2, so I replaced the EM-406 with an Adafruit Ultimate GPS Breakout V3 board (GTPA013 chip), which cites rather lower power requirements - particularly, it runs on 3.3V. I don't have a multimeter at the moment and can't remember the numbers off the top of my head though. IIRC, the Adafruit board draws ~90mA during operation.
This new chip also works correctly with the original Netduino, but cannot find a fix on the N+2. A slight improvement though - it once found a single satellite for about 5 minutes!
I also found this thread which seems to suggest that the N+2 emits enough EMI to mess with GPS. I don't know if this is true, or why the N+2 should be so bad for EMI compared to the original, but could it be a possibility?
I'm going to try running the Adafruit board on the N+2 with an external power supply and see what difference that makes.
Does any of this help?
EDIT: The plot thickens...
- I just ran the Adafruit board on the old Netduino until it picked up 4 satellites.
- I then hot-swapped the TX/RX pins onto the N+2, leaving the power supply coming from the Netduino.
- The GPS continued to spit out $GPGSV string indicating 4 satellites for several iterations.
- I then temporarily unplugged the Netduino, thereby de-powering the GPS.
- When the GPS came back on, it no longer found any fix, even after several minutes (when fully connected to the old Netduino, it picks up at least 1 satellite within about 30 seconds).
I'm not really sure what this means in terms of solving the problem - if anything, it's more confusing!
EDIT 2: I also ran the GPS on the old Netduino with the N+2 powered up next to it. This didn't cause any problems. So if there is any electrical noise issue, it's within the wires.