[Shield Q&A] copota:
I just recently acquired a Shield Portable as well, and of course, now I’m doing the research to get all I can from the device.

When I got mine, I immediately unlocked and rooted it, installed TWRP recovery, flashed the Roth 1.6 updates, and flashed CM12.1 Nightly with Open GApps ARM 5.1 Micro. All went well, and works fine, though I’m still uncertain as to the best recipe to bake my Shield with.

As for your question, how to get back to stock, well, from what I did, it’s actually quite simple.

Take my method with caution!! I’m still new to the Shield, and whenever flashing a device you always run the risk of bricking, so be damn sure you know the do’s and don’ts. Also, this method should completely return you to stock, including removing any custom recovery you installed.

Keep in mind, when I flashed back to stock, my Shields bootloader was unlocked, had a custom recovery, and CM12.1 installed. I’m not quite sure if this makes a difference, I’m just pointing out my configuration at the time.

One last thing, I flashed from a Windows 10 rig, and my instructions will be noob friendly for those that stumble upon this post and need to know what to do from the beginning.

1.	Connect your Shield to your PC, and boot your Shield into Fastboot mode by simultaneously pressing the Back + Home + Shield button. Your shield will boot to a black screen displaying menu options such as Continue, Restart Bootloader, Recovery Mode, among some other options.

2. (SKIP IF SHIELD DRIVERS ARE PROPERLY INSTALLED ON PC) Now, make sure your Shield can be seen on your PC.

In Windows, go into Device Manger, and if there’s an exclamation point next to your Nvidia Shield device (it might read Fastboot device or Roth), then you’ll need to fix that problem so Windows installs the proper drivers.

I’m running Windows 10, and the following method worked for me to get the proper driver installed.

Right click Nvidia device in Device Manager then click the following... Update Driver > Browse My Computer for driver software > Let me pick from a list of device drivers on my computer > Android Device > Android Composite ADB Interface > Click Next and that should install the driver.

3. (SKIP IF SHIELD DRIVERS ARE PROPERLY INSTALLED ON PC) If you have the driver properly installed, you can verify Windows sees your shield by running fastboot devices.

To do this, one method is to download Shield Root files courtesy of CriticalComposer from this link https://www.dropbox.com/s/mr8ro1gx2axynwg/Shield Root.zip

Extract the file, go into Shield > Shield Root. The ABD files are located there.

Press the shift key on your PC keyboard as you right click in that folder, then select “Open command window here”. This will open a command prompt pointing to the Shield Root folder.

Now type fastboot devices in the command prompt and press enter. If Windows sees your Nvidia Shield a serial number will appear. If nothing appears, that means you may not have your Nvidia driver properly installed or in Fastboot Mode.

4. Now that your Shield is connected to your PC and can be seen by Windows, you’ll need to download the Stock image from Nvidia.

Here’s the link https://developer.nvidia.com/gameworksdownload

You might have to create an account to download.

I believe NVIDIA SHIELD Portable Recovery OS Image Update 106 is the latest as of this post. Download it and extract it to your PC.

5. (THIS STEP STARTS THE FLASHING PROCESS) Open the extracted folder, and simply double click flash-all.bat. That should start the flashing process, and it will flash everything needed to return to stock. If it doesn’t start the flashing process, re-check to ensure Windows has the proper drivers installed.

6. Once it completes flashing it will display “press any key to exit” in the DOS box, do that, then reboot your Shield.

7. When your Shield reboots, it should display a screen with NVIDIA and its logo, and might take up to 5 minutes to finish booting.

8. Hopefully all goes well, and you should now be back at stock with Lollipop 5.1 and Nvidia update 106.