The hum you hear is DC voltage on the speaker and that is bad for the speaker, so disconnect the speaker when powering up the amp. At this point I would guess the IC chip is probably a TDA2030 or something similar. The other thread you started on the MEF website had G1 asking you to measure DC voltage at the speaker connection. Do this but remove the speaker first since it probably has DC volts and it's not worth leaving connected at this point. So start by identifying the IC chip in there connected to that heat sink. Look at the top body of the component for a part ID.
P.S. Not sure but that D6 Diode looks like the top leg got smoked a bit?? Please confirm...
P.S. Not sure but that D6 Diode looks like the top leg got smoked a bit?? Please confirm...