The audio jack on my board doesn’t work with headphones and is barely audible with desktop speakers, even when I do the correct startup process (cutoff and octave right, everything else left). Also when using the onboard speaker the sound stops after I turn the volume knob past halfway. Any thoughts or suggestions?
This type of problem is usually caused by a bad connection somewhere in the analog audio side of of the circuit. Start by checking the solder joints on J1. I suggest that you re-flow all of them to make sure they are all good. If that doesn’t work then check (and even re-flow) all you solder joints on the following components:
R14, R15, R16, C8, C10, R19, U3, C9, C3, C4, VR9, R22, C13, C11
Also, make sure there are no solder bridges across any leads.