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.