power on issues while connecting external supply

[hariharan_srm]

HI i am using nordic nrf52840 dk(pca10056) . i am using ble_app_uart example code for my development. i have connected usb in j2 but when i keep my power switch in usb adv led is not blink while keeping only on vdd with j2 on usb supply the ble is advertsing  why?. i want to know how to give external power supply to the board what are the procedures needed to be done whether any jumper switching or any soldering should be done . and how much volatge should be given to external power supply to the board. and then when i connect the nrf52840 tx pin with my lpc controller my lpc controller rx io getting low whether it nordic has been pulling low the io(rxpin) of my controller  

[hariharan_srm]

-->i have flashed nordic_ble_app_uart

-->i have connected the usb to j3 and kept the sw9 to usb 

-->my board is not powering no faint of led also seen 

how to powerup the board using j3 and source mode as usb 

differnece between connecting rhe usb j2 and j3

--> i have been programming and debugging using usb connected to j2 and souce as vdd is this right apporoach