Hello from Costa Rica.
Your problem is the potentiometer of the volume control. At low level, the left channel, due to its age, had became more resistive than the other channel. You must change the pot, and that's it. You can measure the resistance at any point, the left channel should be equal to the right channel or very close. Usually the tracking balance is +-1.5dB between channels when it is correct for the type of integrated amplifier that you have.
If you want to do an updated, you could use a step attenuator:
Happy listening!
Your problem is the potentiometer of the volume control. At low level, the left channel, due to its age, had became more resistive than the other channel. You must change the pot, and that's it. You can measure the resistance at any point, the left channel should be equal to the right channel or very close. Usually the tracking balance is +-1.5dB between channels when it is correct for the type of integrated amplifier that you have.
If you want to do an updated, you could use a step attenuator:
Happy listening!