Thank you very much for your feedback Dust. I checked the boards as thoroughly as possible for solder blobs and everything was clean. You were correct though, it was a hardware problem. The sockets on the RUMBA are upside down. It turns out that I had to invert the connectors of smart controller to board by 180°. To allow me to invert the connectors 180° I had to remove the alignment bumps on thby ChrisM21 - Controllers
I am installing RUMBA board with a smart controller "12864 LCD Smart Controller Display" .on my 3D printer. 1/ configuration.h file: #define REPRAP_DISCOUNT_FULL_GRAPHIC_SMART_CONTROLLER #define SDSUPPORT // Enable SD Card Support in Hardware Console 2/ u8glib has been installed, sketch compiles and uploads with no issue 3/ Cabling has been checked many times and reversed as a check Symptoms:by ChrisM21 - Controllers