First post rockman XPR issue

[Jimmyno]

Hi guys, I'm Giacomo from Italy and this is my first post in this nice and helpful community. 
Here's my problem: i have a Rockman XPR preamp, which is working flawlessly, excepted for the Clean 1.
When i select it alone or mixed with other channels the result i have is a "farty" sound. Strange bass response and even some electrical "zap".
I know that it's not working properly since i have another XPR and now way it sound that way.
My tech and I believe that it might be related to capacitor issues, so we'd start  changing the capacitors involved in that channel.
Can you tell me which ones are in the Clean 1 circuit, or link me a schematic which might drive me straight to the issue?
Thank you.
Ciao
Giacomo