Heres the simple step by step instruction on how to fix a not working microphone on Nokia 5310.
1. Check the microphone visually and using a multimeter* replace if found damaged.
2. Clean the MICs terminal contact pads
3. Trace the outer and inner core MICs contact pads connection line paths.
4. Check/replace the Filter coils and Resistor.
5. If the above procedures doesnt fix the problem* the possible faulty is the PEARL IC. reworking it might only fix the problem.
Nokia 5310 Mic Not Working Solution