i bought a garmin maP62 cheap online. being my first GPS unit i had no idea the 62 does not take an SD card but hass a built in memory of 1.71 g approx. My friend loaded shonky australia topo on the GPSMAP62. It does notb seem to show up on the unit but it is there when i open the map files on the unit using the computer. is there any trick to it being displayed? any suggestions please?