This guide below explains how to fix Unknown Baseband, NULL or Invalid IMEI on Qualcomm devices. Invalid IMEI or unknown Baseband could make your Qualcomm phone unable to receive network signals, make calls or dial USSD codes, access the internet, etc.
What causes Unknown Baseband / IMEI and issues detecting SIM Cards or Network signal on a Qualcomm phone?
The primary cause is the wiping / corruption of the EFS partition(s). This could occur when you:
Format the phone using Chinese box e.g Miracle Box, Volcano Box, Infinity Chinese Miracle II box etc
Flash a custom ROM or not fully incompatible stock rom / firmware
Tamper with your IMEI using an incompatible IMEI changer
Format your partitions (without restoring) via a custom recovery e.g TWRP
Easy steps to fix Unknown Baseband version, NULL or Invalid IMEI and SIM cards / Network signal not detected on a Qualcomm Android phone
Before you proceed, ensure that your Qualcomm phone has a valid Baseband. If your Baseband is UNKNOWN then download the firmware for your model and flash using QFIL . Flashing the firmware (or at least restoring a good EFS backup) ought to restore Baseband. With Baseband regained, you can then proceed with fixing IMEI