Replaced the screen and now the LCD will not turn on

(I'm an ex cellphone repair technician now full time electrical engineering college student, so I had done this repair before, but it had been a while)

I was doing a standard repair yesterday on my sisters iPhone 6s for a LCD replacement and I forgot to disconnect the power to the battery when doing the repair. I did power off the phone before the repair. After putting the phone back together, the phone would turn on but I would not get any display. Fingerprint sensor works, charging works and everything (so I can get the information off the phone) but the screen will not turn on. The screen does come on for about half a second when plugged in the charger for the first time but immediately turns off afterwards.

I believe the issue is on the motherboard since the original screen on the phone does the same thing on the new screen. Possibly a connection was shorted on one of the pins that caused damage to a filter or resistor? Can anyone confirm this?

If the motherboard does have damage can anyone point me to a good business that does motherboard repairs. I live in the Colorado area so if there is a shop in Denver that would be great!