Chosen Solution
I just completed the very long replacement guide “iPad 4 GSM Front Panel Replacement”. The process went relatively well and before I closed up the unit I powered it on and was able to confirm the LCD and digitizer were working and I also logged in successfully and was able to pick up WiFi networks (just to check that the WiFi antenna was okay). Then I proceeded to button up the unit, trying to guide the funny home button ribbon cable as best I could to close it. Now after it was closed and sealed the Apple logo showed for booting but then just stuck there. I tried a hard reboot (with the power and home buttons) and it turned off but then immediately back on again (which isn’t supposed to happen). I thought I damaged the home button ribbon cable so I opened it back up and put in the previous home button cable with the same result. Now I have an iPad which won’t boot. I connected it to my iMac and it was recognized and asked to pair but of course with no interface on the iPad I can’t get much further than that. I also left it overnight and the battery died. Plugging it in I got the same symptom - white Apple logo and nothing more. Hopefully there is an easy solution from you repair gurus out there?
Nope very rare. Only had it happen once on a iPhone 6+ White during screen replacement. Battery got unplugged during Apple logo boot causing the corruption of firmware. Another occurance was an iPhone 5C corrupted itself for no reason week after screen replacement. Both needed restore. Another one was iPhone 6. Corrupted itself when charging overnight. That needed restore too. Had an iPad 4 stuck on Apple logo. Update unbricked it. Actually I’d call it common based on my experience with iOS 10.
Based on what you say, I would assume you pinched or damaged a flex cable during final assembly. Now that you have it open again, I would double check all the connectors and flex cables. If you can, inspect everything with a magnifying glass or jeweler’s loupe. Even tiny scratches or tears to the flex can be problematic. One thing you don’t mention, however, is the battery. Did you disconnect or isolate the battery every time you played around with the flexes, especially the LCD flex. You may have damaged the backlight circuit. As @benjamen50 suggests, perhaps it is just a firmware problem so worst case, you could try DFU Mode if data retention is not an issue.
