USB connection is broken and "Check USB" shows in the window.
How do I operate the amp?
Thank you for your comments, have you used the UBS before?, please make sure its the correct cable, a mini USB data cable , not a charging cable, if you still have an issue we would suggest the amp is looked at by an engineer.
As your question was "How do I operate the amp?" I've got good news for you: Marshall CODE is one of a few modelling amps, where absolutely ALL features are fully accesible without any external device.