I hard bricked my friend's w8 last week by unlocking bootloader via mssm7227_semc because I forgot to check the manufacture date (clumsy me) .. it had 12W01 under the battery
So, I search around the internet, digging and reading many forum posts and articles and finally I managed to revive it with omnius (just revive it - never want to try unlock bootloader again on this unit because have no credit on my omnius acct plus had to lend him my hd2 as temporary phone - ouch) .... I had to get a nokia ca-42 cable and build a UART cable out of it (my cable only has 3 wire so it helps me find the rx,tx and gnd quickly). With the help of omnius (I have one month license but no credit - so I guess one day license should be sufficient), I use repair s1-boot function with testpoint and manage to fix it after 2nd attempt.
Therefore, if anyone had hard brick x8/w8 after unlocking bootloader, you can try repair s1-boot with omnius. The only difficult thing to do is to solder those wires to the board (I tried using tape but didn't work for me - suspect loose connection)
below is the log from omnius (for safety purpose, I remove imei and device id from the log):
11:21:36 Repair S1-boot
11:21:36 Repairs the S1-boot via UART.
11:21:36 Operating system: Microsoft Windows XP Home Edition Service Pack 3 (build 2600)
11:21:36 Application version: 1.38.4753
11:21:36 . The action name is 'Repair'
11:21:36 Selected phone type: W8 Walkman.
11:21:36 Selected connection method: UART ROM
11:21:36 i Instructions
11:21:36 i 1. Make sure the phone battery is charged to at least 50%.
11:21:36 i 2. Switch off the phone!
11:21:36 i 3. Remove the phone battery and wait at least 5 seconds, then insert the battery back to the phone!
11:21:36 i 4. Connect UART pins according to the documentation!
11:21:36 i 5. Connect the testpoint to phone's ground (battery negative pole, metallic circuit shielding, GND) and leave it connected!
11:21:36 i 6. (A connection to the testpoint (TP) is not needed when the boot is erased.)
11:21:36 i 7. Shortly press the power button!
11:21:36 i 8. Disconnect the testpoint!
11:21:36 i 9. Click Activate next to the cable icon!
11:21:36 . The action started waiting for the user
11:22:07 . The action finished waiting for the user
11:22:07 Connecting via PL-2303 USB Serial Port (COM24)...
11:22:07 Device driver version: 188.8.131.52
11:22:07 Establishing connection to the phone...
11:22:07 Connection established.
11:22:07 ID: 06010080900000
11:22:08 Sending loader...
11:22:12 Waiting for loader response...
11:22:14 Sending loader...
11:22:23 Waiting for loader response...
11:22:24 IMEI: - remove -
11:22:24 Device ID: - remove -
11:22:24 Minimum loader AID: 0001
11:22:24 Color: Brown
11:22:25 i Waiting for connection to the server...
11:22:29 Receiving news...
11:22:29 i News
11:22:29 i Omnius for Samsung v1.18 - Experimental unlock code read for Samsung Galaxy S II and similar, FREE
during test period
11:22:29 i Omnius 1 Year licenses purchased after 1st Oct 2011 now gained
unlimited android unlocking!
11:22:34 Writing S1 boot.
11:22:50 s Successfully done.
11:22:50 . The action entered shutdown phase
11:22:50 . The action reported success
16 40 F8 B0 DF 9A 0F B4 83 80 C5 D8 C9 16 E3 CD
only using 4 wires (3 from ca-42 and 1 loose wire for test point) + omnius account, no need jtag/box. no need micro usb too.
4 - Testpoint - loose wire to ground (I tape it to sim holder and release after pressing power button)
5 - ignore this - no need to attach wire
6 - TX from ca-42
7 - RX from ca-42
8 - GND from ca-42
Try disconnect the ca-42 cable from the usb first before removing the battery after it's finished because on my 1st attempt, the battery fell off while ca-42 cable still plugged in usb resulting no boot. (no idea if it was because of the battery or my mistake)
Once the phone is detected after plugging in the micro usb cable, I simply flash the original 2.1 fw (can download from omnius server if you don't have it - need to use omnius acct detail to login and download). I did this to check if all the functions are good (wifi/signal/camera/gps/etc), then proceed with rooting and install recovery.
Now the phone is alive again with locked bootloader (as long as it's not broken, it's good enough) and currently running gingerdx v028b fw .. horaaayyyy!
My special thanks to Omnius for wonderful software solution and to gingerdx team for wonderful fw that can run on stock kernel.
Wish you all the best in reviving your hard bricked x8/w8
attach is how to connect wires + test point :