Fixing an iMac's malfunctioning internal microphone can often be done with software updates and by deleting the preferences. An iMac's internal microphone is used to capture sound for audio and video chats or music and vocal recordings. The microphone is built into the body of the computer and cannot be removed without opening the case, an action that may void your warranty or cause further computer problems.
Click the "System Preferences" icon in your "Dock," then click the "Sound" icon.
Select "Input" from the "Sound" window toolbar and verify that your "Internal Microphone" is active and unmuted. You can edit your microphone's audio levels using the sliders below the active devices list.
Mute any currently active microphones besides the "Internal Microphone." External microphones connected to your computer may interfere with your internal microphone's ability to capture and record sound.
Click the "Apple" logo on your toolbar to begin installing new software updates and drivers. Click "Software Update." Your iMac will connect to Apple's servers and locate any new updates. Out-of-date software drivers may be one of the causes of malfunctioning hardware.
Restart your iMac by clicking the "Apple" logo and then clicking "Shut Down." Click "Shut Down" again when a new window pops up. Wait until your iMac has fully powered down, then press and hold the power button to turn the computer back on.
Click "Macintosh HD," "Library" then "Preferences" to delete your old "Sound" preferences. Click the "Audio" folder and select both "com.apple.audio.DeviceSettings.plist" and "com.apple.audio.SystemSettings.plist" and drag them to the "Trash." Press "Ctrl" and click the "Trash" icon. Click on "Empty Trash."
Run "Apple Hardware Test" by shutting down your iMac, disconnecting all devices, except your USB keyboard and mouse, and restarting your iMac while pressing the "D" key. Select your preferred language from the "Apple Hardware Test" screen and follow the on-screen instructions. Note down any error codes or messages the test produces.
If problems with your internal mic continue, schedule a "Genius Bar" reservation at your local "Apple Retail Store" via Apple's website. A visit to the "Genius Bar" lets you meet with a trained Apple expert and, if necessary, schedule a repair. Check the status of your warranty at Apple's website. "Genius Bar" appointments and repairs are often covered by your iMac's warranty or protection plan.
You will void your iMac's warranty if you open the case and attempt at-home repairs.