One of the main problems with Android devices when it comes to access the recovery mode to do a hard reset and leave as manufactured is that the devices are not standard and each manufacturer removed or put buttons at will, why they did this little list of how to enter recovery mode Android
Let's start with the most normal, tablet or smartphone with volume keys
Press Volume + and boron ignition for 10 seconds
Press Volume +, Volume - and power button for 10 seconds
Press Volume - and power button for 10 seconds
Tablet or smartphone with volume buttons and home button
Press Volume + home button and power button for 10 seconds
Press Volume +, Volume -, home button and power button for 10 seconds
Press Volume - home button and power button for 10 seconds
Tablet or smartphone without volume buttons and button Home
Press home button and power button for 10 seconds
Tablet or smartphone without volume button without home button
Press the power button for 20 seconds
We hope this list helps them to your android devices