The left channel output in the amplifier stage is going out - could be a cold solder connection due to overheating. Check the left channel output of the power transistors solder trace - you can compare them to the right channel stage because they're almost identical circuits.
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The left channel output in the amplifier stage is going out - could be a cold solder connection due to overheating. Check the left channel output of the power transistors solder trace - you can compare them to the right channel stage because they're almost identical circuits.