Well it's been quite a voyage..
Got my TF201 returned from RMA yesterday, it works fabulous - let's work it with Unlock Tool.
Gives me unknown error. What could that mean? After some lurking I find my s/n is "unknown". What's that? Maybe it can't authenticate with the Asus servers? After more investigation I find various s/n unknown threads and stumble upon the Ratchet fix for this. Sure I thought.
But Ratchet required root, so first a downgrade (I used 184.108.40.206). Then hard wipe to clean the new firmware from previous garbage data.
Next use mempodroid to gain temporary root access and apply the s/n fix according to the guide
Allright, serial number pops up in settings.
Let's try OTA and Unlock Tool to confirm success - none work.
Unlock Tool still displays "Unknown error. This may be a network connection issue. please wait and try again later.".
That seems like a short story. Well for documentation here's the howto to what was done:
- Settings - Applications - Manage - All - DMClient - Force Close/Clear Data/Clear Cache and then reboot. Next, go to Settings - About - Check for update.
- Soft factory reset - factory reset from within android settings.
- Hard reset - When device is off perform the following: "vol down+power button" -> "vol down button" -> "choose wipe by toggling with vol down button" -> "confirm by pressing vol up button twice"
- Manual downgrade - Use Method 2. Downgrades regardless of previous SKU (WW/US/TB etc.) and previous firmware version. Perform a hard reset to cleanup after flash. Enable "USB debugging" under "Developer options" in settings and get familiar with ADB to do this.
- Fix serial number with Ratchet - Chronologically I used the s/n restore guide here. Since the the TF201 is downgraded, the temporary root exploit described in the guide will work.
- root - (Optional) - It was attempted simply because it was possible at this stage, although futile if the next step is performed, even with OTA Rootkeeper.
(Choose (1) or (2))
- (1)Manual update - make sure SKU of new firmware matches currently possessed SKU. Any root access after performing this step is gone.
- (2)Manual update and keep root without s/n - (Experimental) - Apparently some people have attempted to manually write the incremental OTA Updates to /cache/ partition and force update - thereby keeping root. However, even by reading the posts I cannot grasp how, and it was a heart-attack inducing experience. Not recommended.
I have tried the above with "US_epad-user-220.127.116.11" and "WW_epad-user-18.104.22.168" downgrades, upon which I upgraded them to their corresponding SKU (important).
Beginning the attempts with "WW_epad-user-22.214.171.124" I now rest on "US_epad-user-126.96.36.199".
Maybe this will work for somebody, it did not for me, but I am far from being bricked and await another RMA to resolve the issue. I am incredibly happy with Asus' support and what they do for the community. A sincere thank you to Gary Key who kindly forwarded me to some very knowledgeable people.
Hope this is of use to somebody!