that's a pretty easy thing to diagnose. id say 9/10 times its a disconnect in the audio wire.
The labor, on the other hand, is usually extensive.
-Youll need to open the device, and disassemble the device nearly all the way.
-Start by verifying no cold joints on the soldering points of the speakers, and connecting wires. apply fresh solder to all joints, and test.
-Check the continuity on the wire going through the band. if thats not connecting properly, replace that wire.
-Verify speaker function. Put a low voltage, mid-frequency signal into the speaker to verify sound output. if it doesn't buzz, you will likely have to replace the speaker.
usually, it is one of the above that cause the issue, however, it is possible to have a board level failure.