I recently converted my Wanhao D6 (Monoprice IIIP) to Smoothie board as the original controller would crash intermittently.
All is fine and the machine works better than it ever has the entire time I have owned it.
However on occasion the display on the GLCD will scramble with two bands of hash across the screen if the OctoPi is connected to the USB port. If I start it with the USB cord not connected it never happens.
Thinking electrical issues I taped over the 5V+ pin in the USB connector to no avail. It is kind of a PITA to have to plug in the USB cord after powering up the Printer and OctoPi.