It could be that the signal is being dragged down by the EQ chip but hoping for an easier solution I replaced each of the three capacitors in turn feeding into that chip C24 (which looks like it had been replaced before), C33 and finally C74. The signal on R75 is zero volts, so there is nothing going into the EQ chip for the left channel. The signal on R74 on schematic shows a good signal that then feeds into the EQ chip and on to the AMP chip and out to the right hand speaker. The paths to the headphones also show good signal both left and right as expected. The paths to left and right audio show a good signal. Here is what I have found so far with the oscilloscope. > If any component involving a heat sink is worked on, be sure to thoroughly clean the heat contact surfaces and carefully apply new heat transfer compound. If there are faulty components there, you may be able to source replacements from your cracked board. Check all components and PCB traces from there to the left speaker out. > Find where the signal path splits into separate circuitry towards the headphone out vs speaker outs. > Does the headphone out jack switch off the speakers? In that case, check if the switch in the jack is faulty, keeping the left speaker off all the time. If the same applies to your Korg board, that would mean a lot of it is already good. In my Onkyo amplifiers, the signal path for the headphones out is largely shared with the speakers' path. The audio outs and headphones now working is great news. The image of the schematic is not that readable, so I can't say much about that. Clever move, this already is a nice accomplishment!
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