Here are some potential issues to check:
1. Check the fader control: Make sure the fader control is not turned all the way to the front or rear speakers, as this could prevent sound from coming out of the main speakers.
2. Inspect the speaker wires: Ensure the speaker wires are properly connected to the amplifier and speakers. Loose or damaged wires can cause sound issues.
3. Check the head unit: If the amplifier is working properly, verify that the head unit is sending an audio signal. Try adjusting the volume and balance controls on the head unit and see if the sound improves.
4. Inspect the ground connection: Ensure that the amplifier has a good ground connection. A poor ground connection can cause sound issues.
5. Test the speakers: Disconnect the speakers from the amplifier and connect a known-working speaker directly to the amplifier output. If the sound works with the known-working speaker, then the issue may lie with the original speakers.