IPHONE STUCK ON BOOT SCREEN? HERE'S WHAT I FOUND...
I recently did a repair on an iPhone 3GS that took nearly 3 weeks to figure out. When I thought I was finished, the iPhone would stay stuck on the Apple logo boot screen and would not budge. This is what I discovered during this repair.
First off, we started with an iPhone 3GS that had a cracked screen. It belonged to a friend of mine, and resulted from dropping to a hard surface. An attempt was made to replace the screen, but to no avail.
I took the phone home to the man cave, and tore it down. The first thing I noticed was that the digitizer cable plug (labeled #2) was not securely snapped into the motherboard. This is a common problem in iPhone screen repairs. When the plug is not securely seated into the board, it will not work.
The reason the plug didn't fit is due to the fact that it was a replacement digitizer for an iPhone 3G, not a 3GS. Plug #2 is not the same on these devices. But the difference is so minute, it's not totally obvious when you go to installing the new digitizer.
I replaced the replacement screen with a correct screen, one made for a 3GS. The cable plug snapped right in, and I reassembled the phone. But I ran into the problem of the iPhone staying stuck on the boot screen that displays the Apple logo.
After sitting for 5 minutes, you get the winding clock animated icon, and nothing happens after that. I did some research, and found that a solution would be a device reset from connecting to a computer (with iTunes).
I was lucky enough to load iOS 5.1 (it formerly had iOS 4) and reload the entire iPhone. But it still had problems staying stuck on the boot screen. Nowhere on the web did I find any more advice on this issue. So I decided to tear the phone down again.
I discovered the problem. My thought was that there was still a problem with one of the cable plugs. As it turns out, plug #1 that slides into the slot on the board, the one that connects the LCD, was not secure. During the failed attempt to install the wrong digitizer, the housing around this plug was chipped away.
I carefully reinstalled this cable, lowered the clamp lever, and then reconnected plugs #2 and #3. After putting all the pieces together, I found immediate success. iOS5.1 was installed and running, and there was no delay in the Apple logo boot screen at all.
If you're having similar problems with the stuck Apple logo screen, a device reset from a computer is required. You need to wipe it fully and start from scratch. But any more difficulty in booting the device is probably due to a loose or damaged cable connector.
I'm surprised that there isn't more information on this issue out on the web. I hope people suffering from this issue find my post helpful. It's quite a frustrating problem to figure out.
I'd like to hear from any fellow iPhone-fixing geeks if they've run into this and discovered the same root problems that I have. Share your experiences in the comments section!