[G Tablet Q&A, Help & Troubleshooting] Misty soul:
unbricked!

I finally got the device unbricked.

Since I always got messages about full BCT, I finally decided to try to reset it with nvflash --rawdeviewrite. The BCT is at the very beginning of the memory (from block 0 included to block 1536 excluded). It starts with 16 bytes of magic numbers: b380 6840 476e 15b9 23f1 5b07 18d2 8a58, followed by 16 bytes set to 0, followed by the 4080 bytes you find in the various bct files lying around these threads. This pattern seems to be repeated several times, each 64k, so I thought it could hold several configuration (1536 blocks of 2048 bytes each can hold a bunch of such 64k sections).

So I forged a first 64k block from the magick numbers, the zeros, my Malata_a02_12Mhz_H5PS1G83EFR-S6C_333Mhz_1GB_2K8Nand_HY27UF084G2B-TP.bct file and filled the rest with ffff. I wrote this to the tablet and ... it did only write a long series of ffff. So I have finally completely overwritten my BCT with garbage :(

After that, almost all nvflash operations failed, even simply downloading the bootloader. Error messages were either bad data, or missing partition table, or BCT related.

I tried several bootloaders, fastboot.bin from an ac100 thread the bootloader from the dropbox link in Roebeet's thread here: http://xdaforums.com/showpost.php?p=9603803&postcount=1, and the one from the Malata image in nvflash_t2_mp_wifi_1202.rar. This last one succeeded. Since I had already used this commands a very large number of times and it always failed before, I think this time it succeeded because I had erased the BCT with my bunch of ffff.

Here are the final command I set and its output:

sudo ../nvflash --bl bootloader.bin --bct Malata_a02_12Mhz_H5PS1G83EFR-S6C_333Mhz_1GB_2K8Nand_HY27UF084G2B-TP.bct --setbct --configfile an
droid_fastboot_full.cfg --odmdata 0xbb0c0011 --create --go
Nvflash started
rcm version 0X20001
System Information:
chip name: t20
chip id: 0x20 major: 1 minor: 3
chip sku: 0x8
chip uid: 0x17144040432025d7
macrovision: disabled
hdcp: enabled
sbk burned: false
dk burned: false
boot device: nand
operating mode: 3
device config strap: 0
device config fuse: 0
sdram config strap: 0

sending file: Malata_a02_12Mhz_H5PS1G83EFR-S6C_333Mhz_1GB_2K8Nand_HY27UF084G2B-TP.bct
- 4080/4080 bytes sent
Malata_a02_12Mhz_H5PS1G83EFR-S6C_333Mhz_1GB_2K8Nand_HY27UF084G2B-TP.bct sent successfully
odm data: 0xbb0c0011
downloading bootloader -- load address: 0x108000 entry point: 0x108000
sending file: bootloader.bin
| 928956/928956 bytes sent
bootloader.bin sent successfully
waiting for bootloader to initialize
bootloader downloaded successfully
setting device: 1 0
creating partition: BCT
creating partition: PT
creating partition: EBT
creating partition: NVC
creating partition: MBT
creating partition: BLO
creating partition: MSC
creating partition: KLO
creating partition: OGO
creating partition: SOS
creating partition: LNX
creating partition: APP
creating partition: CAC
Formatting partition 2 BCT please wait.. done!
Formatting partition 3 PT please wait.. done!
Formatting partition 4 EBT please wait.. done!
Formatting partition 5 NVC please wait.. done!
Formatting partition 6 MBT please wait.. done!
Formatting partition 7 BLO please wait.. done!
Formatting partition 8 MSC please wait.. done!
Formatting partition 9 KLO please wait.. done!
Formatting partition 10 OGO please wait.. done!
Formatting partition 11 SOS please wait.. done!
Formatting partition 12 LNX please wait.. done!
Formatting partition 13 APP please wait.. done!
Formatting partition 14 CAC please wait.. done!
done!
sending file: bootloader.bin
| 928956/928956 bytes sent
bootloader.bin sent successfully
sending file: bootloader.bin
| 928956/928956 bytes sent
bootloader.bin sent successfully
sending file: mbtdata.img
- 1024/1024 bytes sent
mbtdata.img sent successfully
sending file: boot.bmp
- 1843254/1843254 bytes sent
boot.bmp sent successfully
sending file: boot.bmp
- 1843254/1843254 bytes sent
boot.bmp sent successfully
sending file: logodata.img
| 418176/418176 bytes sent
logodata.img sent successfully
sending file: recovery.img
/ 3362816/3362816 bytes sent
recovery.img sent successfully
sending file: boot.img
| 2758656/2758656 bytes sent
boot.img sent successfully
sending file: system.img
- 152334336/152334336 bytes sent
system.img sent successfully

After that, the tablet rebooted automatically, with the Malata logo.

Last few problems were that it was in chinese and with the touch screen not responding. The touch screen problem was due to not understanding the slider at the bottom of the initialization screen was an unlocking slider and should be moved to activate the touch screen. Then I had to search a little to reset the tablet in english.

The last few days have been tiresome, and I would have appreciated getting some help here ...