Chosen Solution
Just bought a new screen and battery for my iPhone 5s. Just replaced both pieces following tutorials and everything went ok. The phone just turned on and apparently everything was working. However, when I started using the phone I noticed that the screen turns off when opening any app. If I lock and unlock the phone, it works again. If open another app, the screen turns off. Based on this, I’d say it seems that the battery does not have enough power to keep the screen on…? Does anyone faced this issue? Any hint? Thank you!
Sounds like a bad screen, never had this happen from anything else other than a faulty replacement screen. Try reseating the screen connectors if that does not help contact iFixit support for a warranty replacement.
