[XDA Assist] daver68:
I previously posted in the local Galaxy S3 i747M section with the same problem, but now the issue is worse than before.

Here's my previous thread:

http://xdaforums.com/galaxy-s3-att/help/boot-loop-plugged-to-ac-twrp-wipe-data-t3070064

A note that I'm no stranger to flashing and the inner workings of Android architecture (ROMs and general hardware), . But for the sake of this issue, please feel free to treat me like a noob if you think it would help elaborate any procedures I should follow or troubleshooting steps I should take, or just throw ideas at me like the software dev that I am and expect me to figure it out on my own.

Some background:

Recently (around beginning of April), my phone began to exhibit strange behaviour - reboots when reading/writing from internal memory (not uSD card), unable to wipe /data partition in TWRP or CWM. I would also get bootloops when I was plugged into direct AC charging (no problems if plugged into a computer for charging, though).

When in TWRP, CWM, and Philz, I would not be able to wipe the /data partition or anything in it. Installing anything to /system also caused a crash (though wiping it didn't cause any issues). Doing a factory reset wipe would also cause the recovery to "crash" - the recovery would freeze up and the phone would reboot. I could not restore a NANdroid, I could not install a new custom ROM. In TWRP, if I opened up a terminal window and manually tried to repair the /data and /system partitions with the e2fsck command, it would still freeze up and crash.

At that point, I downloaded the stock 4.4 firmware image (I think it was NF2?) from Sam Mobile and flashed it via Download Mode + Odin. Booted it up and ran the phone stock for probably a week. Then, I carefully used Odin to flash a freshly downloaded (and MD5 verified) TWRP 2.8.6.0 TAR image and SuperSU. Flashed both via Odin just fine. From there, I mounted the microSD card - I didn't want to touch the internal memory for now - and copied over a fresh downloaded copy of a CM12 based ROM (also MD5 verf'd) to it. From there, still in TWRP, I successfully flashed a 4.4.x TouchWiz-based ROM.

Take note that at this point, doing anything to attempt to wipe /data still leads to crashing the recovery. Nothing I have done has resolved this issue. I left that issue alone, just happy to have a working phone.

That above procedure seemed to work. I could then use the phone for about 2 weeks. Then my phone started crashing again, same as before: only when I was doing something that was reading/writing the internal memory. E.g. music, podcasts, etc.

I followed the same procedure with Odin + stock firmware > reboot > Odin + TWRP + SuperSU > flash custom ROM. Worked fine again for 2 more weeks.

Here I am 1 month later, same problem as the last 2 times. This time, however, after flashing the custom ROM, it does not boot up now. My phone is at home because I cannot use it. Last night, upon trying to boot up S3rx and PAC 5.1, I literally let it sit at the boot animation for 1 hour, each, and neither got past the boot animation. I'm familiar with ROMs sometimes taking say 10 minutes upon very first boot on a clean flash, but I gave up after about 1 hour (in fact, 1.5 hours for PAC 5.1, which was my second attempt last night). It's to the point where I'm certain if I left my phone plugged into the AC, it would still be at the boot animation over 12 hours later.

I know of the NAND memory corruption issue that S3's had previously, and I did flash the stock firmware that came out at the time (I think it was an Lxx based bootloader+firmware). But that was years ago, end of 2012 if memory serves me correct.

Thoughts on what I am facing? What I should try and do next? Where to go from here? If this is a hardware issue that is beyond fixing with flashing things in fastboot/ADB/Odin, then I'll face defeat and look for a new phone. But if I can hang on to this phone for just a little bit longer...

Thanks!