If you bought an A2 28.4MHs Scrypt Miner this guide will show you how to change the voltage from 220V to 110V for your power supply.
First you need to identify the top of the machine, it will be the one with the least amount of screws, and it will only be 4 screws on each corner. Such as shown in this picture:
Then you will unscrew these and take off the top of the miner, after this you will see the insides of the A2 miner. The power supply is the device that is attached to the side of the case which is circled:
After you open the top of the case and identify where the power supply is you will need to unscrew the power supply from the case. To do this look on the side of the case where the power supply is and unscrew the 4 screws that are holding the power supply in place, the ones that I have circled:
Now the power supply is unscrewed and you are able to freely move it around, try not to unplug it from anything and make sure that you remember that the fan goes on the side without the case so that it can breathe:
The 110v and 220v switch will be located on one of the long sides of the power supply, just flip it around and you will be able to see the switch, if your switch is on 220v it will look like this:
To change the voltage to 110v, simply use your finger nail or anything else that is able to reach the switch and flip it to the other side so the white line is on the 110v side. It will look like this after you flip the switch:
Now all you have to do is screw everything back in, making sure the fan faces outwards and not towards the case where you are screwing the power supply in, and you can plug in your A2 miner and it should be on the right voltage!