KOrg PA 800 - Sound distortion FIX

[Grzmn]

Goodmorning to everyone, I'm a PA800 owner.
I return cyclically to this forum to understand how to solve this well known problem of the PA series. In recent months I have read many solutions. After advising me to change the motherboard (300 euros) it seems that the problem is due to the malfunction of some resistors (much lower cost).

Yet, there is NOT a SIMPLE AND CLEAR guide for doing this job. Can we do it together, maybe starting from who has already solved the problem?

I don't think that will damaged Korg (that PA keyboards have manufacturing problems has always been clear) or the repairers. Moreover, even spare parts are often nowhere to be found and assistance does not make replacements.

Thanks, I ask for your help.