1. Check and clean buzzer / ringer connector
2. Check buzzer / ringer, replace buzzer if needed
3. If the problem not solved, check L152 and L151, resolder and replace if needed
4. If the problem not solved, check C164, resolder and replace if needed
5. If the problem not solved, check R161, R162, resolder and replac if needed
6. If the problem still not solved, check ringer IC / N150
7. If the problem still not solved probably UEM fail/broken, resolder and replace UEM if needed
8. If the problem not solved, circuit broken trace circuit , make jumper or swap engine
