Chosen Solution
Phone cut off on me during daily use, failed to come back on afterwards. Tried recovery power on, usb to itunes from computer and even letting it charge for some time and still nothing.
Tried replacing the battery as well but it still won’t come on and at this point I’m beginning to think the board has crashed or something but I would love to get another diagnostic opinion and what’s the next best move from here
I would start by testing a bare-bones setup. Start by disconnecting the battery first (always!). Then disconnect the digitizer, LCD, front camera, rear camera and home button extension flex (see this guide). Now re-connect the battery; you should only have the battery and Lightning Dock flex connected. Connect a known-good, preferably Apple-original Lightning cable to an iTunes enabled computer. If you have access to a multimeter, you could measure the battery first. If it reads ~3.8V - 4.2V, then it is good. Does iTunes recognize your phone? If so, then you should re-connect one flex at a time until the phone stops working. I would start with the Home button flex first, then add the rear camera, LCD & Digitizer then from camera flex. If the bare-bones setup does not get recognized by iTunes, then you most likely have a logic board issue. You could send it (or find a local) to a repair shop that specializes in micro-soldering repair. Sometimes the fix can be straightforward (i.e. a blown filter) and relatively economical.
