How do I know my motherboard is damaged?
So I took my iphone 3gs to a phone repair shop. At first I thought it was the battery, but after replacing the battery twice, MY PHONE IS STILL SHUTTING OFF. It won't even stay on for 1 minute until it shuts off and restarts with apple logo. The guys at the phone repair shop said that the motherboard isn't working properly. I just want to know if the motherboard is the cause of my iphone going on and off. If not then what could be the problem? Any help is appreciated. Thanks.
iPhone 3GS, iOS 6