Chosen Solution
I have an iPhone 5s that desperately needed a new battery. About a week ago, it turned off and when I plugged it in, it would go into an endless reboot cycle: the apple logo would appear, a red screen would flash for 1/4 second, screen goes black, and the apple logo appears again. From what I’ve read, this could have been a battery issue and/or a logic board issue. I figured I’d start with the battery. I ordered a new battery from iFixit, installed it today, and turned on the phone. I got the same reboot cycle but this time, it would happen without being plugged in. I tried to do a force restart but all that accomplished was turning the phone off so it wouldn’t go into the boot cycle. I tried putting in DFU mode but iTunes could not update the phone- it gave me the 4013 error when it tried to update the software. At this point, I tried opening up the phone again to make sure that I had everything connected properly. Everything looked fine, so I closed it up again and now the phone is completely dead. I get nothing on the screen at all, no apple logo or red screen, even if I plug it in. Force restart does nothing and DFU mode is just like before- iTunes recognizes theres a device there but can’t do anything with it. I’m thinking I must have damaged some screen connections? For what it’s worth, they look OK. If I knew for certain that this were a logic board issue, I’d just buy a new board but I’m not so sure that is the case- or at least the only problem at this point. Any ideas on why I’m getting absolutely no response from the phone?
I tried diagnosing the 5S with the exact same symptoms and issues you were having. I wasn’t able to fix it even after replacing the charging chip (U2 Tristar), attempt to restore the iPhone, replace battery and charging dock. Red Screen on 5S generally points to a bad eMMC (Flash memory that stores iOS firmware and user data) chip basically in short, the phone is fubar. I’m guessing you already tried booting up the phone with the front camera ribbon cable unplugged as that can cause red screen on boot?
