My SainSmart Megatronics 2.0 encountered a short circuit due to a bad crimp on one of the external display ribbon cables. Since then, it will only run from USB power. I never wasted my time troubleshooting it.
If I interpret the top left corner of the schematics page correctly, IC2 is probably the 5V voltage regulator, since pin #3 of that device is connected directly to pin #2 of the SRC12v jumper pins. I assume that you have not Googled for the Megatronics 2.0 schematics or data sheet downloads on RepRapDiscount.com's web site, and strongly recommend that you download both since the data sheet shows pictures of the board with all connector labels at the beginning as well as the defective mask missing several pin labels that SainSmart unfortunately put into production at the end. That picture at the beginning that shows all of the correct pin labels saved my board from getting trashed by mis-wired endstops.....
If I interpret the top left corner of the schematics page correctly, IC2 is probably the 5V voltage regulator, since pin #3 of that device is connected directly to pin #2 of the SRC12v jumper pins. I assume that you have not Googled for the Megatronics 2.0 schematics or data sheet downloads on RepRapDiscount.com's web site, and strongly recommend that you download both since the data sheet shows pictures of the board with all connector labels at the beginning as well as the defective mask missing several pin labels that SainSmart unfortunately put into production at the end. That picture at the beginning that shows all of the correct pin labels saved my board from getting trashed by mis-wired endstops.....