[Galaxy S III I9305 (4G LTE + 2GB RAM) Q&A, Help & ] sagie:
Background, Symptoms and Repair Attempts

My significant other's I9305 spontaneously died. The phone is fully stock, non-rooted. Was never custom-flashed.

It was working with no apparent problems, then one night we left it (turned on) to recharge overnight, as we usually do, and found it boot-looping in the morning.

"Boot-looping": repeatedly showing "Samsung Galaxy S3" screen for about 4 seconds, then restarts (screen goes black for about 3 seconds, then "Samsung Galaxy S3" screen shows again, infinitely repeating).

The boot-loop prevents access to recovery mode or to the main OS.

"Charge mode" is working - when phone is turned off, it shows charge animation when connected to power source (with battery level rising as charging progresses).

Download mode itself is accessible, and phone remains in it until I force it to end. Text shown on top of download mode screen:

ODIN MODE
PRODUCT NAME: GT-I9305
CUSTOM BINARY DOWNLOAD: No
CURRENT BINARY: Samsung Official
SYSTEM STATUS: Custom

However, actual flashing is apparently impossible. I tried several times using Odin v3.09 to flash 2 different stock images:

I9305XXBME3_I9305DBTBMF1_I9305XXBME1 (Stock 4.1.2)

I9305XXUFNL1_I9305DBTFNL1_I9305XXUFOA1 (Stock 4.4.4)

In all my flashing attempts I had only "AP", "Auto Reboot" and "F. Reset Time" checkboxes checked, and the rest unchecked.

All attempts failed (with a red "FAIL!" on the top-left of the window) within 2-3 seconds after clicking the "Start" button. Odin's message log for such an attempt is as follows:

<OSM> Enter CS for MD5..
<OSM> Check MD5.. Do not unplug the cable..
<OSM> Please wait..
<OSM> I9305XXBME3_I9305DBTBMF1_I9305XXBME1_HOME.tar.md5 is valid.
<OSM> Checking MD5 finished Sucessfully..
<OSM> Leave CS..
<ID:0/004> Added!!
<ID:0/004> Odin v.3 engine (ID:4)..
<ID:0/004> File analysis..
<ID:0/004> SetupConnection..
<ID:0/004> Initialzation..
<ID:0/004> Get PIT for mapping..
<ID:0/004> Firmware update start..
<ID:0/004> SingleDownload.
<ID:0/004> tz.img
<ID:0/004> NAND Write Start!!
<ID:0/004> FAIL!
<ID:0/004>
<ID:0/004> Complete(Write) operation failed.
<OSM> All threads completed. (succeed 0 / failed 1)

I also tried using Odin to flash 2 different custom recovery images:

openrecovery-twrp-3.0.2-1-i9305-F2FS

CWM_touch_6.0.4.7_i9305

Attempts to flash these failed in the exact same way as the stock images did (as described above).

Despite all my (failed) flashing attempts, all symptoms remained unchanged (boot loops, no recovery, only download mode and charge mode working).

Questions

I'd really appreciate any tips, advice, or answers to the following questions:

Are these symptoms indicating a problem with the eMMC chip?

Is there any possible repair other than replacing the eMMC chip? Is there any chance for repair using a dedicated JTAG/eMMC tool?

Am I supposed to be able to salvage at least part of the data on the eMMC chip using an SD reader and an SD adapter soldered to the motherboard (e.g. in a manner similar to the process described here)?

Am I supposed to be able to salvage at least part of the data on the eMMC chip using a dedicated JTAG/eMMC tool? Would I be able to extract more data with such a tool than I would be able to extract using the soldered SD adapter and reader?

Many thanks in advance for your time and help efforts!