Microsoft confirmed the temporary setback for Windows Phone 7.8 update for Nokia Lumia 800 due to some minor issues, including battery drainage problem and data update failure. But using NaviFirmPlus allows manual installation of the Windows Phone 7.8 update.
The manual update for your Nokia Lumia 800 requires NaviFirmPlus which can easily be searched from Google and the Nokia Care Suite application.
Disclaimer: The methods and tools mentioned in this guide belong to their respective owners and developers. Performing a manual update can damage your device. Do the appropriate research before proceeding. The developers are not responsible for any errors which may happen to your device.
Warning: This procedure can void the device's warranty and may also erase all data files. Make sure to backup the contents of your device. Do this at your own risk.
1. Download NaviFirmPlus 1.7. You can search the tool online.
2. Download and install Nokia Care Suite on your computer. If you have any compatible issues with C++ or any other similar programming language, use the older version of the suite.
3. Check your Nokia Lumia 800 model by looking on the SIM tray at the back of your phone. Alternatively, connect the device via USB cable and launch the Nokia Care Suite. Double click on the "Product Support Tool for Store" and view a new window will display the "Type Designator" and "Product Code." Note both details.
4. Launch NaviFirm Plus 1.7.
5. Search for the Nokia Lumia 800 with the same Type Designator of your device. Select under the "Releases" tab the code "1750.823.8858.12460" which is the Windows Phone 7.8 update.
6. Choose any variants from the list. The variants contain several different language according to their region but has the same update content. You can change the language later.
7. Then click "Download". The program will create a new folder named "Fw" or Firmware inside the NaviFirmPlus 1.7 folder.
8. Double the "Fw" folder and you will see the downloaded firmware. Open that folder.
9. Rename some details of the three files with extensions ".dcp", ".vpl", and "_signature.bin". Replace details only with the model number and product code, and leave everything as it is. [Model no._Productcode_XXXXXXXX.dcp]
10. Once you have finished renaming them, copy all the files in the folder. Go to your main drive and look for "ProgramData." It is usually hidden, and you can unhide it by going to the Folder Options.
11. Open the "ProgramData" folder. Go to Nokia > Packages > Products > [Model number] and paste the files you have copied here. Create the Packages, Products and the model number folder if they do not exist. Remember to name it exactly as the model number, otherwise the suite won't recognise it.
12. Go back to the Nokia Care Suite and make sure the device is connected. Click the cube like icon at the bottom right of the window and select "Rescan data packages." The icon will turn green.
13. Click "Programming > Refurbish." The current and new software version will be displayed. Click "Start" to begin installation.
When the installation is complete, you can now disconnect the device from the computer.
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