I bought a restored all-LED Pinbot a few months ago. It works, but there is an audible 50 Hz hum (I am located in Europe, therefore 230V/50Hz power) coming through the speakers. The volume of the hum always stays the same no matter how the volume knob is set. Lights have no effect to the sound of the hum - it's always pure 50 Hz.

In order to get rid of it I replaced all 8 caps on the power supply board (see shiny new blue caps on the picture) but unfortunately there is no improvement.

What else could I try?

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Unfortunately I haven't got an O-scope. Where is the audio cables shield pin? Would you please mark it on a picture? Thank you.