DEAD GoPro hero 3+ black, 4 silver & black

[1centchips]

I am in possession of new but out of warranty GoPros. All of them are like new cosmetic condition including the main board. All of them have not power. I have tried plugging into a charger with a good know battery. I have also followed all of the instructions listed on the gopro support website. I was hoping if I could revive them by microsoldering and replacing components. I did not find any schematics for these. Any help is appreciated!

[Rasz]

well, start measuring then 

[SL4P]

See if you can find out their history... were they returns, failed during warranty, power supply reversed etc.
Then, since you're obviously inside already... connect the external supply, and chase the +v to see if it gets into the main board...
SMT fuses, protection diodes... etc
If you don't know what these look like, then try posting some high quality images of the board - and if that fails possibly calling GoPro for an RMA number.

[Seekonk]

Simplest test is do they draw any power at all.  No current would indicate something with regulator section.