iPhone 6s won't turn on possible short due to power outage?

Hello all,

So this iphone 6s I have had for a long time. I replaced the screen and other components and it was working fine. Then through a power outage one day the phone would not turn on. I went through the usual initial checks (cables out, anything looked burnt) but nothing. I don’t think its the screen because I just replaced it and when I connect it to my PC there is no read. But when I connect it to a portable battery I can see the battery is pulling power. So I was able to rule out the battery that was faulty, which I also replaced within the year. My question is what to try to troubleshoot so i do not break the bank, my initial thought is replacing the logic board. I do not want to order a ton of parts and break the bank. If anyone has any ideas on how to begin to trouble shoot this, I would really appreciate it. Happy holidays!