Turn on your phone and watch for any smoke, strange noises, or burning smells. Check the battery and look for any swelling.
Test all the buttons and features (such as the microphone, speakers, wireless connectivity, camera, etc.).
Note any component or feature that doesn’t seem to be working. If anything isn’t working, disassemble the phone and check for obvious problems, such as a broken logic board component or corrosion on the cable contacts—or even an error in reassembly.