I've been using a 4D Systems OLED screen for an arduino project and I've come across a problem with getting the screen to start up when using an external power supply.
I've switched to use the software serial library and found the screen would only start up if the usb cable was plugged in.
I later discovered that the cable only had to be touching the housing of the socket for it to start.
I've tried all sorts of combinations of power and data pins for the screen. I've tried different start up delays to let the screen settle. I've also tried using different power supples with no joy.
The screen /is/ powered and /will/ work without the usb cable connected as once the screen is started the usb cable can be removed and it will continue to work. It's just convincing the screen that it's plugged into somthing I guess.