NEW 3DS XL Wont turn on issue ???

Check your ribbon cables and your fuses.

 

This issue is well documented, and the ribbon cables are typically always the problem. Check to make sure there are no tears and that they are all seated properly. Try powering on the system while the top screen is hinged at different angles. The only other thing that typically causes this problem is a damaged LCD, but considering you replaced the daughterboard the ribbon cables are most likely your problem. Check the one connected to the top screen.

 

I would, because that's the only thing I can think would cause the problem. Or you could wait around to see if other people have any ideas.

 

The issue seems to come from top screen ribbons which are not correctly inserted or maybe torn.

Try to see if the both top and bottom LCD flashes or just one of the two.

 

Ok so the matter is surely with the Power ribbon of bottom screen.
Check the black connector, this one should not be raised.

If it was raised, remove the ribbon and attempt to reasonably press it to get a better constraint.
Especially be careful to not break it.

 

Same issue after removing the motherboard.
Dumb question, is the 3 ribbon cables that connect the top screen, is there a guide that shows which cable goes where? Or is it as obvious as it looks.
Also, how would you know if it's the fuses or the ribbon cables?

 

What screen flashes ?
The screen that flashes is ok, the matter will be with the other so check the ribbons of it.

 

Your problem has to do with the three ribbons in the corner. You have the longest one back words. Flip it and it should work

 

thank you it helped me