iPhone 7 doesn't turn on after replacing battery, screen and dockconn.

I have an old iPhone 7 that has been laying around for quite a while. Since there's still some data on the phone that i'd like to retrieve i tried fixing the phone a couple of times. In the process of tinkering around for fun i broke the screen and the battery cables. So i decided to buy a new battery, a new screen and a new dock connector. I replaced those parts a couple of days ago.

Now, however, the phone doesn't turn on at all. When i press the power button nothing happens; when i connect the phone to the charger, nothing happens either. I thought i had replaced all the broken parts, but perhaps the logic board itself is broken? If so, how could i check this?

Thanks in advance!