1970-01-01 02:00:00 timestamp on log-files?

Why do I sometimes (50% of times) get the date 1970-02-02 in Mission Planner when I have connected the controller to the computer to download logs via USB-cable? Its in the windows where I choose which log to download.

Bad GPS data, date and time are missing so you have the default.


Ah, so the battery in the GPS is bad?
But it works sometimes.
Should I leave it on for a while for it to update the calendar?
Where do I see if the GPS data is correct and the date is there in Mission Planner?

How is this solved? The problem is still there. How do I fix it? =)