Step 9: U2/U4 Fix
What causes this? While the cause is not completely determined, one reason may be charging your completely discharged battery.
In most cases, both the U2 AND the U4 mosfet need to be replaced. This part will not only fix it, but make your Roomba less susceptible to this type of damage in the future. http://www.mouser.com/ProductDetail/STMicroelectronics/STN3PF06/?qs=du%252bo5tJIeNKF3dCiL6LdRg%3D%3D The whole procedure should only cost 3 dollars!
To remove and install this part, a SMD Rework Station will be used. (An Aoyue) Just use your hot air soldering iron to desolder the part, dispose of the part so you don't get it mixed up, then put solder paste on the pads and install your Mouser part. The Parts you need to be replaced are on different sides of the board, and labeled U2 and U4 hence the name. First picture is of U2, second is U4. Schematic made by RobotReviews Member Gordon: http://mysite.verizon.net/gsplews/misc-pix/charging_n_control_schema.GIF
To reassemble, just follow the steps backwards.