Korg Pa500 Master Volume Silder 0, Right Speaker 100% always

[Nikosaek2121]

Hello my korg Pa500 Right Speaker always play audio no matter where the master Volume Slider is, the speaker is always 100%. Master volume only effects the left speaker. Could this be software issue or hardware ? I have thr unit open because I'm fixing my keys, can someone suggest me a solution to try ? Could this be software issue or hardware ?

I tried other speaker ( I have a defective unit for parts ) same happens
Tried cleaning the potentiometer with alcohol from outside still same