820-3476 on then off

[tech]

820-3476 board turns on for second just showing apple logo then shutsoff ,
also not turning on with power button (not keyboard issue).
just power on while connecting charger.

 

[2informaticos]

Check if you can turn it on/off with R5151/16 pads, instead of power button.
If not, check SMC_ONOFF_L level, w/ and w/o keyboard connected.
Impropper/unstable signal can force the board off.