If you notice any software malfunctions with your YXTel W666 android device, you're most likely required to download and flash stock ROM firmware on your W666 to permanently correct the software errors you noticed on your YXTel W666. And when you load stock firmware on your YXTel W666 using any Qualcomm flash tool, your YXTel W666 will be reset to factory defaults settings and by that, definately, your UserData will be lost including contacts, messages and others.
If your device has been bricked and want to unbrick it, you will need to pay closer attention to the tutorials contained below here.
YXTel W666 Stock ROM Firmware Download Link(s)
How to Flash Stock Firmware On YXTel W666
1. Download your YXTel W666 stock ROM firmware from the link above.
2. Extract the YXTel W666 Firmware you downloaded from the link above onto a folder on your PC.
3. Download and install Qualcomm android device drivers on your PC. You may skip this step if you have installed Qualcomm drivers on your PC already otherwise, download Qualcomm drivers here
4. Now, choose either of the tools listed below here to load the stock firmware on your YXTel W666.
Note
1. Each of the tools listed above contained step by step guides with illustrated pictures on how to flash stock firmware on your YXTel W666.
2. If your device is bricked already, I recommend that you use Tool Studio eMMC Download Tool or QPST QFIL.
3. If you require any further assistance, simply drop your comment detailing the issue(s) and I shall help you revive your YXTel W666, if need be.