Have you got v3.50 fw? It had shutdown issues. From the Garmin changelog:

Changes made from version 3.50 to 3.60:

Fixed issues that could potentially cause memory corruptions and unit shutdowns.
Upgrade to current v3.90 if you have an earlier version but 1690 is region specific so make sure you use the correct region fw. See [Only registered and activated users can see links. ].