J2 - Shared power jumper. Pins 1 and 2 jumped. J3 - Configuration jumper. S1 S8 - Servos. The servo board responds to the following commands.
Second byte is the module address.
Third byte is the servo address. This board is factory set to board address 2 and 19200 baud rate. To reset the board to the factory defaults place jumper in J3 pins 1,2 and power off then on. Move the jumper back to the center off position. When changing the board address or baud rate place the jumper in J3 pins 2,3 and then send the software change command and then power down.