To view service menu on etrex...
hold down the PAGE and PAGE UP buttons while you power up. The unit will enter the service mode and display:
Tech info
Bravo Version
Software Version
Time
Internal temperature of unit
Battery voltage
External voltage
Button presses
You can do a LCD screen check by pressing the PAGE button twice
Pressing "up"+"enter"+"on/off" keys in service mode will reset the eTrex to factory defaults. All presets and data will be lost.
To exit just turn it off as normal, and then turn it back on as normal.