Screen not working after replacement, tested with 4 others

I have an iPhone 6 that I'm attempting to repair. The phone was forgotten on the top of a car and it fell off while the car was in motion. The damage was extensive, however it did show signs of life (eg, vibrating motor worked) I've completely replaced the housing and which was slightly bent at the top but not very much. When I tested a new screen, it started with the backlight not powering on but I could just faintly make out the apple logo. I then tested with another screen and was able to get full functionality but only while the screen was angled upwards. Two more screens later, I now don't get anything from the screen. I've inspected the logic board but can't find any obvious damage. Any ideas?