Verify that the volume setting is correct in Sound preferences (Mac OS X) or the Sound control panel (Mac OS 9).

Verify that the computer is not set to Mute. Press the Mute key on the Apple keyboard.

Reset parameter random-access memory (PRAM). Press and hold Command-Option-P-R during startup until you hear the startup sound twice.

Test the computer with known-good headphones. Do you get sound?

Yes: Go to the next step.

No: Replace the main logic board.

Verify that the speaker cable is connected.

Replace the speaker assembly.

Replace the logic board.

Verify the issue with known-good headphones.

Verify that the computer is not set to Mute. Press the Mute key on the Apple keyboard.

Verify that the volume setting is correct in Sound preferences (Mac OS X) or the Sound control panel (Mac OS 9). If the preferences are set correctly, replace the logic board.

In Mac OS 9, check the Sound control panel's Speakers tab.

When headphones are connected, a headphone icon is present. If the headphone jack is malfunctioning, it may indicate that headphones are connected when none are connected. In this case, replace the logic board.