Farfisa syntorchestra 4 mono and brass problem

[miledas]

Hello synth lovers
I'm working on Farfisa syntorchestra 4. it couldn't power on but when i change power unit i was able to get sound from poly section. In this device ''mono'' and ''Poly'' section has seperate pcb boards.
The poly section is fine except brass preset which is quite and distorted. I think all presets has own eprom chips for store sound. But this is my idea, can't sure whitout service manual

But mono section is fully silenced
I checked mono card's components there is no problem on the board i think. also checked ribbon cable connections connected on chip and preset buttons.

Does anyone know about these devices or have a service manual ???