The handset will not show fine detail at max res i.e. when zooming in I just get lines of main routes etc. Any ideas?
Remove and reseat mSD card. Often fixes it.
Check
Menu>Menu>Setup>Maps>[4th tab across]>Menu>'Show All' (ie, display all available mapping)
Check
Menu>Menu>Setup>Maps>[1st tab]>Detail 'Show More' (ie, show 'more' detail - 'most' is OTT I find)
Failing that, and assuming that the map is correctly located at
[card]\Garmin\gmapsupp.imgSuspect a corrupt map file, it does happen.
Failing that, try a Full Reset of the Etrex
Full Reset (but this means going through all your settings again after the reset so it's definitely a last resort).
(NB in the above shorthand,
Menu means 'press L-H button' )