To fix or repair mic problem on Nokia 2690, you may first check the microphone module using a multimeter or replace it with a new one to securely confirm that the microphone is still working or not damaged.
If the Microphone is okay, clean the mic's terminal contact pads. Refer to the solution below and do some check and test procedures.
Nokia 2690 Mic Problem Repair Solution
If the mic module is okay and the filter components already been replaced but still the problem occurred.
The problem then may possibly lies on AVILMA IC. Reheat it adequately. if it doesn't help, rework it and then replace if necessary. This option may only help fix the Nokia 2690 not working mic problem.