Sometimes after flashing/upgrading and mtk device, the device ends up having no signal from network provider which is a result of corrupted imei number. If you dail *#06#, you will discover that the imei number is null or invalid. To fix this problem we can easily use the popular MTK Engineering app but it works only on some android OS (Android 5.1 and below) and also only when the baseband of the device is OK. The following tutorial below will show you how to fix imei problems of mtk devices including fixing of baseband issues. This tool is way better than all the others.
Change of imei number is illegal
Do this at your own risk!
MTK VCOM Drivers
MAUI META 3G
BP Modem database file of your device