3DS Mainboard not receiving power

Hi all, I've repaired a few 3DS consoles recently but come across another today that looks immaculate. No signs of drops, no water damage. Looks brand new on the outside and inside!

Overview of the problem: 3DS Charges fine, but wont power on at all. No life from it when the power button is pressed.

I've checked the 3DS with another mainboard and it works flawlessly, so it's definitely the mainboard that's the issue. Also ruled out the wifi module, IR module and SD Reader, all working fine in another 3DS.

Checked both the fuses with a multimeter, they're fine.

Checked the power button (SW1 on mainboard) and also seems fine.

Note: Not sure if this helps but I do notice when the orange charging light is on and you press the power button there's a very slight flicker from the charging light. This doesn't happen with another working 3DS I have.

Out of ideas now... Any ideas anyone? Or is it time to give up?