Hi Marcel,
If I understand it, searching for "NanoVNA doesn't want to start" in forum discussions may be a solution. It's a good idea to read these and it might help. As far as I remember, there was mention of increasing the capacitance of the electrolytic capacitor.
I note that you refer to the white Gekko as ttrftech as an official supplier.
Remember, ttrftech is named after the original idea host (@ edy555). It was the business of the clone manufacturers and their dealers to steal this.
Use the Search Button.
I wish you a successful search and repair.
73, Gyula HA3HZ
Gyula Molnar