Hi Pierre – can you provide a good, clear solder-side photo as well? Besides good, clear, close-up photos from several angles and all sides, another good bit of info to share when requesting help is a list of voltage readings on the voltage supply, IC pins and any transistor pins. On another point, 90% of issues are simple soldering mistakes – either by cold\incomplete solder joints, solder-bridges, component orientation, or unintentionally swapped wiring.
What we cannot see is the stompswitch and its wiring to the main board. That might prove helpful as well. From what I can see in the photo you have provided, it appears that R10, R5, R15 & C3 appear to be somewhat starved of solder. I’d start by reflowing the solder on those 4 components and carefully examine all other components for good solder flow to both sides of the PCB. Hope this helps.