The following requirements used to install test builds on Lumia devices are listed below:
- The MainOS partition of the build that the user wishes to install
- The partition can be extracted from a build's FFU using the Dump function in WPInternals.
- The device's stock FFU
- A copy of Windows Phone Internals
- A copy of the Windows Phone Common Packaging Tools and the EFIESP update packages from build 14393
- The Windows Device Recovery Tool app for its drivers
- Devices such as the Lumia 640 must be on build 10586 before doing this process.
- This guide is not responsible for any bricked phones done in the process and is specifically targeted towards Lumia devices. It is first recommended to perform a full backup of the Lumia using Win32DiskImager before proceeding. The desired build's EFIESP should also never be flashed directly, as that can result in a permament brick as well.
- This guide also assumes that
C:\ is the user's Windows disk partition and that G:\ is the Lumia's MainOS partition.
- This method of installing Windows 10 Mobile builds will only work if the desired FFU is designed for the same device that the user is planning to install it on, and will not work if it is flashed to another device. For example, build 14262 (rs1_shell_winhub) can only be installed on production Lumia 950s, while build 10587 will only work on production Lumia 640/640XL's. Builds designed for engineering boards such as the Hapanero (RX-130) will also not work on production hardware.
- It is not recommended to use this method on builds prior to build 10586.
These instructions assume that the user has already installed Windows Device Recovery Tool, the WP Common Packaging Tools and extracted the EFIESP packages to an easily accessible place.
With the Lumia powered off, select "Interrupt boot process" in WPInternals and connect the phone to a computer. Once the Lumia is in flash mode, select the Lumia's stock FFU in the "Flash original FFU" option of the Flash menu in WPInternals, and then click Flash. Once the phone restarts, complete the out-of-box experience like normal.
Once the OOBE is completed, navigate to C:\Program Files (x86)\Windows Kits\10\Tools\bin\i386 in an elevated command prompt window and execute the following command:
iutool -V -p C:\path\to\efiesp\cab\files
After the phone updates, turn off the phone and select "Interrupt boot process" in WPInternals, then unlock the Lumia's bootloader. Once unlocked, select "Manual mode" in WPInternals and then "Boot mass storage mode", after which execute the following commands in the same command prompt window as before:
bcdedit /store G:\EFIESP\EFI\Microsoft\Boot\BCD /set {default} FLIGHTSIGNING on
bcdedit /store G:\EFIESP\EFI\Microsoft\Boot\BCD /set {bootmgr} FLIGHTSIGNING on
bcdedit /store G:\EFIESP\EFI\Microsoft\Boot\BCD /set {default} TESTSIGNING on
bcdedit /store G:\EFIESP\EFI\Microsoft\Boot\BCD /set {bootmgr} TESTSIGNING on
After doing so, hold down the Power and Volume down buttons on the Lumia to power it off and interrupt the boot process in WPInternals again. Navigate to "Flash" -> "Flash seperate partitions", and flash the MainOS partition of the build wished to be installed. Once the flash is done and the Lumia is restarting, hold down the Volume down button. The Lumia should show an exclamation mark on the screen. Then, press these keys in the following order: Volume up, Volume down, Power button, Volume down. The Lumia will now attempt to reset the phone, but will fail on the first attempt. After restarting, it will try again and succeed.
Complete the out-of-box experience by normal means.
