may be try to change sim or try factory reset or go to service centre to update software
if your phone is older then 1 year i suggest to not to change mother board because it is very costly better to add some money and change phone or sell old phone for exchange offer
"Thanks for being with Samsung and for sharing your. Let me recommend some steps to further isolate and determine what you are experiencing. Please be aware that device speeds may vary based on multiple outside factors. We would like to suggest you kindly follow the below mention steps to overcome the Issue:- 1) Ensure that network frequency of your device should be selected on Auto-mode. Menu>Settings> Connections>More Networks> Mobile Networks> Network Mode> Select Auto mode (GSM/WCDMA/LTE). 2) Search for the Network Manually as follows: Menu> Settings> Connections>More Networks> Mobile Networks> Network Operators> Select Manual Search. 3) You may check by exchanging the SIM in SIM slots. 4) Insert different SIM card in your mobile and check if the issue is resolved or not. If still issue persists then we would suggest you to once contact with your service provider. "
