If you're lazy and don't care for manuals, like a buddy of mine, I wrote this little procedure to get him started with a fresh SD card in addition to a factory reset (this was actually intended for a 436, but should be pretty much identical):
1. Remove the batteries. To remove the SD card, with your fingertip, slide the metal bracket in the direction of the UNLOCK arrow while pushing down slightly. When unlocked, the card and bracket will pop up. Gently slide it out of the bracket.
2. Flip the bracket up. Carefully slide the new card into the bracket, contacts facing out, making sure the card is secured by the little tabs on each side of the bracket. Swing the bracket back down and lock the card in place by reversing the removal process. Put the batteries back into the scanner and power it up.
3. An SD card error message will display, connect the scanner to your computer via USB (mass storage mode should auto-select)
4. Load Sentinel, select Update > Update Master Database, then go to Tools > Select Target Model. Make sure SDS100 is checked.
5. Next, go to Scanner > Clear User Data, check the “display all drives” box and hit OK
6. Hit OK two additional times and Sentinel should say “writing to scanner”
7. When the message displays “finished clearing…”, hit OK
8. The scanner is now completely wiped and in the default (out-of-the-box) state. Unmount the scanner (right-click USB icon in tray, then click Eject Device – if it can’t unmount, wait 30 seconds and try again). Once unmounted (“can now be safely removed” message), you can disconnect the USB cable.
If you want to use it in this state, when powered up it will say “Nothing to Scan”. At this time you may want to go through basic settings by going to MENU > Settings (here you can make the key beep quieter, set clock, etc.). The backlight defaults to OFF (good to save battery). To enable it, go to MENU > Display Options > Set Backlight > Set Mode > Squelch and select the amount of time to hold the light when a transmission is received, then hit the ENTER (either push down on the rotary control or hit the “E” key) then move to Keypress and do the same, then Timeout and select a maximum time for the backlight. Exit with the SYSTEM button or back out by hitting the MENU button repeatedly until it resumes scanning.
9. Hit the MENU button > Set Your Location > Enter ZIP Code > US, complete the ZIP field then hit ENTER
10. The scanner will now auto-load anything it’s able to receive within the set range (default is 20 miles, change it by going to MENU > Set Your Location > Set Range, complete the field then hit ENTER
11. An alternative to zip code scanning is to attach the GPS antenna accessory (useful for road trips). The range setting also applies in this case (usually best left to a small value).
12. Once all your settings are complete, it will be scanning just default service types (EMS Dispatch, Fire Dispatch, Law Dispatch and Multi-Dispatch). To add/remove Service Types, hit MENU > Select Service Types. You can now toggle all available types ON or OFF. Exit with the SYSTEM button or back out by hitting the MENU button repeatedly until it resumes scanning.
13. To load a custom scanner setup (aka “Profile”, this includes all settings and favorites lists), after STEP 6 (finished clearing message), in Sentinel, go to File > Open, select the desired profile and hit OK. Next, go to Scanner > Write to Scanner, a box will pop up showing the scanner drive letter and name (SDS100 and ESN) highlighted in blue. Check the “erase favorites lists” box, then hit OK twice.
14. Or, to back up all your current settings, click Scanner > Read from Scanner
15. A popup should display showing drive letter, scanner model and ESN. Hit OK.
16. When finished, hit OK again. Unmount the scanner.
17. Go to File > Save to save the profile (might have to click “Create New Profile”). The name you saved for the profile should now be displayed in the top left corner of the window. The scanner is now backed up to your computer and can be restored simply by selecting 'write to scanner' (handy to correct accidental changes or in situations where the scanner is acting strange).