Vintage Korg CX3 with noisy 50hz

[Bortolo]

Hello everyone!
I'm new to the forum and I'm not too strong with English.
I am an Italian boy passionate about music and vintage instruments.

As a title I own a Korg CX3 that works very well but has always had annoying 50Hz in the output.

Here I found the schemes:
http://robertweatherford.com/bx3/schematics.htm

I have already disassembled the keyboard and changed all the electrolytic capacitors which were visually damaged and also the 12V regulator.
The hum and a white noise has decreased but still quite present, I think it is generated before the "over drive" stage since if I turn the potentiometer the noise increases.

I would exclude a failure on the KLM-245 board as the noise persists even when it is disconnected.

Would anyone know how to help me or have they already dealt with similar problems?

[Drawbar Dave]

I've repaired a few of these and also the BX3 version. I would turn my attention to the mixing board and PSU board below the drawbars. After a recapping on one CX3 for a customer, I had damaged a solder trace and found it using an audio probe. Carefully inspect the back of both boards to see if a dry solder joint is affecting a ground connection. I have also had broken wires to pots on these. The most annoying board to remove and inspect as you probably know is the one with the tact switches on it. Another place to check for broken wires is on the back panel. Because it is hinged and moveable, sometimes a wire comes loose. Look at cleaning the connections in the shorting jacks of the effects send and return or try a jack jumper cable between them to see if there is a dirty contact there.

[Bortolo]

Thank you
Now I am checking all the ground connections on the power supply board.
The next step will be to check the solder joints on the mixing board.