dead iPhone after overheat

[e_p_a_k]

okay it all started when i had my iPhone plugged into the USB port of my laptop because my laptop was tethered to my 3G connection. i didn't notice that it was getting a bit hot, until eventually it gave me a pop-up saying something like "your iPhone has become hot. you can only use it once it has cooled down" or similar to that.

so i let it lie for a couple of hours until it was cool to the touch again. wouldn't turn on. figured the battery was drained. plugged it into the wall socket, let it charge for a bit, then it turned on by itself. to my surprise, it gave me the activation screen. okay, no biggie, i'll just reactivate then, fine. so i unplugged it (upon which it immediately died), and tried plugging it into my laptop. i guess the power from the laptop wasn't enough to keep it on, as it wouldn't stay on long enough to boot and be detected by iTunes. okay, so i'll plug it into the wall socket longer, i thought.

this is when i really started to worry. i noticed that it would intermittently reset while plugged into the wall socket. from the activation screen, it would search for a signal, not be able to latch on, and then reset. rinse and repeat. i started freaking out when it wouldn't even stay on but would just constantly repeatedly reboot over and over again. so on the activation screen, i pressed the little "i" icon above the "slide to unlock" bar. i'm not so sure what usually gets displayed there, but i assume it's something along the lines of the IMEI etc. well, pressing it would give me a blank pop-up.

alright, panic mode. last resort - unplugged the iPhone (immediately turned off), fired up iTunes, plugged it in. it's able to boot into recovery mode (good) and is detected by iTunes as a phone in recovery (good!). keeping fingers crossed, i attempt to restore it. no dice. i'm getting an error 21 on iTunes. tried it with a rebooted computer, multiple USB ports, and different cables. no go. error 21 each and every time, and when i unplug the iPhone, it immediately powers off.

finally, i replaced the battery (had a technician do it), but it's now stuck on recovery mode. updating via iTunes using a stock IPSW gets me an error 21. i'm using a stock USB cable that came with my iPhone. tried both in recover mode and in DFU mode. in DFU mode, it goes through the motions, then eventually restarts in recovery mode, and that's when it hits error 21.

tried again: different computer, different USB, fresh download of iOS6. still error 21. my phone's dead, isn't it?

i'm using a carrier-locked iPhone 4, never jailbroken.

[dbleug22990]

Have you tried to restore from a different computer?

What OS are you using?

Do you have TinyUmbrella installed?

Error 21 is usually fixed by dfu mode. Are you positive you got it into dfu mode?

[e_p_a_k]

yup. i tried multiple computers, multiple USB cables, running unjailbroken iOS6 so I don't have TinyUmbrella installed.

yes, definitely DFU mode - blank, black screen, but read on iTunes as a device in recovery mode.

[iRevival]

Once in DFU mode put it into Pwned DFU mode with redsn0w and try to restore again. Also make sure your hosts aren't pointing to the Cydia servers instead of the apple servers.

[blkcadi]

Error 21; These errors typically occur when security software interferes with the restore and update process. Follow Troubleshooting security software issues to resolve this issue. In rare cases, these errors may be a hardware issue. If the errors persist on another computer, the device may need service.

[e_p_a_k]

my iPhone isn't jailbroken, so i don't think it's Cydia-related though.

[blkcadi]

If you followed my iTunes troubleshooting link and still have the same issue, seems to be a hardware issue. Since your battery was replaced, could something may of been overlooked/unplugged or damaged?

I understand you have no Cydia, I read your first post, I think the other poster was perhaps assuming you were.

[Cowboy]

What kind of battery did you install? If its a cheap knock off it may cause that problem.
IS the phone actually getting hot or just giving the warning? if it is getting hot can you give me an idea on where it is getting warm?

[e_p_a_k]

the battery replacement wasn't the cause of the problem - it was one of the steps i took to remedy the initial problem.

previously, it would get warm. in fact, it got really hot which was why it died in the first place. the entire back plate would get hot.

upon changing the battery, it would no longer get warm.