[Xperia Arc General] sengoku:
s1tool wouldn't unlock bootloader for me and after trying for some time i found a solution that worked for me so i though i would post it up as it might be an issue that someone ells could experience too.

have follow the guide exactly and s1tool would work up until.

see log

DETACH USB CABLE FROM PHONE

REMOVE BATTERY FROM PHONE

ATTACH TESTPOINT

PRESS "READY", THEN ATTACH USB CABLE TO PHONE

DETACH USB CABLE FROM PHONE

REMOVE BATTERY FROM PHONE

ATTACH TESTPOINT

PRESS “READY”, THEN ATTACH USB CABLE TO PHONE

PROCESSING …

REMOVE TESTPOINT NOW, THEN PRESS “READY”

TO CONNECT NEXT PHONES

X10 Xperia,E10 Mini,E15 Xperia X8,U20 Mini Pro

LT15 Xperia ARC,MT15 Xperia NEO,R800 Xperia PLAY

PRESS AND HOLD “BACK” BUTTON…

ST18 Xperia RAY,ST15 Xperia Mini,SK17 Xperia Mini Pro

PRESS AND HOLD “Volume Down” BUTTON…

PLEASE ATTACH TURNED OFF PHONE NOW

RUNNING S1_EROM VER “R9A028″

SOFTWARE AID: 0001

LOADER AID: 0001

FATAL ERROR [ SECURITY_CLASS, SIN_header_verification_failed ]

error while uploading HDR block

LOADER NOT STARTED

Elapsed:64 secs.

First i though well the just try to flash bootloader it might still work as the last part with reconnecting while pressing back on arc was never mentioned in the guide on first page.

but although i was able to boot into fastboot mode i could not flash bootloader.

see log

12/025/2012 01:25:36 - INFO - Device connected in fastboot mode

12/025/2012 01:25:40 - INFO - Selected kernel (boot.img or kernel.sin): C:\Flashtool\firmwares\boot.img

12/025/2012 01:25:40 - INFO - Flashing selected kernel

12/025/2012 01:25:40 - INFO - FASTBOOT Output:

sending 'boot' (5850 KB)...

FAILED (remote: The Device must be rooted first)

finished. total time: 0.001s

so i tried again to unlock bootloader with some small variations to when and how to connect phone till one method just magically worked.

in s1tool and in the guide you are asked to remove battery and connect test point, but i would not work for me. \

so here is how to fix..

1 remove battery

2 insert battery

3 phone must still be off.

4 select in s1tool to patch boot.

5 s1tool asks for test point.

6 put needle to testpoint / gnd

7 press ready in s1tool

8 s1tool starts scaning / now insert usb cable while still holding test point.

9 s1tool confirms found testpoint and asks to remove testpoint.

10 remove testpoint

11 press ready

12 s1tool finishes processes / this is where i would be stuck

PLEASE ATTACH TURNED OFF PHONE NOW

but if you simply have battery in your phone when processes starts i simply finds phone as soon as you press on ready

see log..

DETACH USB CABLE FROM PHONE

REMOVE BATTERY FROM PHONE

ATTACH TESTPOINT

PRESS "READY", THEN ATTACH USB CABLE TO PHONE

PROCESSING ...

REMOVE TESTPOINT NOW, THEN PRESS "READY"

TO CONNECT NEXT PHONES

X10 Xperia,E10 Mini,E15 Xperia X8,U20 Mini Pro

LT15 Xperia ARC,MT15 Xperia NEO,R800 Xperia PLAY

PRESS AND HOLD "BACK" BUTTON...

ST18 Xperia RAY,ST15 Xperia Mini,SK17 Xperia Mini Pro

PRESS AND HOLD "Volume Down" BUTTON...

PLEASE ATTACH TURNED OFF PHONE NOW

RUNNING S1_LOADER VER "R4A062"

LOADER AID: 0001

FLASH ID: "002C/00B3"

LOADER VERSION: "r4A069"

SEMC SIMLOCK CERTIFICATE, PROCEEDING

FINISHED

Elapsed:16 secs.

:victory: