1st Switch off your device, now remove the battery or sim card &Put it again. Thenturning on the phone.& wait for few second if signal not found in your device. First check the imei number. By typing (*#06#) in your mobile keypad and you get the 15 digit unique mobile identity number. The imei no create communication between mobile device and network provider through a sim card. Sometime its automatically erase/ delete, and as result no signal in mobile device.
If issue due to imei number missing then you can easily fix the issue by write imei.
I had described below some components which are majorly failure in a no network mobile phone.
1st Check the antenna connector: – its rusty, open or dry antenna is major part to receive & distribute signal over the air or open space. Every mobile phone antenna has 2 pin. One pin connects with negative connection or another one connects RX/TX circuit through a gsm tester jig or external antenna connector.
2nd if antenna or gsm tester jigs both are ok. Then problem happen either RX or TX circuit. RX Circuit use for receiving the signal, and the TX circuit use for send a single.
Now follow the process to conform which area is faulty. Put the battery in your device and turning on the phone then go to settings >> network settings >> network mode manual >> search for network if you found network provider name that means the RX circuit working fine and it’s ok . If can not found any network or service provider that means fault due to RX circuit.
after found the network provider/service provider name now select home network. If don’t able to select network that means fault due TX circuit. If both are ok then check the related components and replace if required.