Hey!
I bought my iPhone X for 100€ on “eBay Kleinanzeigen” (the equivalent to craigslist) . The Screen was shattered at one corner and it had the iTunes-logo showing up.
This thread here is great and helped solving my problem, BUT:
When you can turn it on without the earpiece, it isn´t necessarily a logic board fault!!!
It might just be sweat that got into the earpiece assembly and corroded something.
I just cleaned the earpiece assembly with some alcohol et voila: it worked!
If it doesn´t work out with your phone, just try this: https://youtu.be/JM-04aWOVnw
I hope that I was able to help.
Greetings from Germany!