Leaderboard

I can't remember what the resistance is of the volume control pot but at maximum volume you will have approximately 60 Ohms load so half the power will be dissipated in the 27 Ohm resistor. I think the 10 Ohm is to stop the sound being turned off completely.

It depends on what sounds are being generated. This isn't very helpful I know but as you have no sound at all it shouldn't matter. What you could try is to disconnect the green plug then switch on as this will generate an alarm. Then you can check all those outputs from the two chips to see which one (if any) has a waveform on it. If you can't find anything I'll set it up here and let you know for sure which chip sends the alarm tone. Putting two speakers in series is a good idea, just make sure you put them in phase.