Why is my MIC no longer working after upper case replaced?

I would talk with your service tech or vendor who performed the repair. The microphones are in the upper case on the left side (facing the keyboard normally) near the speakers and should be functional. If you paid for the repair with a credit card let them know you have a dispute with the vendor (better than hiring a lawyer and going to small claims court-the credit card company can pressure the vendor to do it right.)

As a work around a USB microphone dongle (most have a built in mic and line in/out ports) will work temporarily. USB audio is separate from analog audio.

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