Won't turn on or charge, have replaced battery and charging board

I would suggest ordering a USB amp meter. This will give much needed information.

Your current should be at about 0.12amp ish with fluctuations with the battery disconected. And anywhere between 0.45 to 1.2-1.6amp with the battery connected depending on the battery voltage.

A steady eading of 0.45 amp with the battery disconecting is often a sign of a short or failed IC.

If so the motherboard may need to be repaired. Replacing it would also be an option if you don’t want to repair the circuit board.

I’ve seen a fair bit of galaxy s8, and s7 with failed power IC. And usually they read 0.45amp with the battery disconected.

This post is 2 years old, but if someone have the same problem, here is the solution I found.

I had the same problem on my Samsung Galaxy A51, I changed the battery and the charging port but my phone still wasn't charging. I found that in my case the problem came from the flex cable connecting the charging port to the motherboard (the big orange one with the phone model written on it). I changed it and my phone is now charging normally!