I purchased a FRDM-KEAZ128Q80 from DigiKey. The OpenSDA portion of the board appears to be nonfunctional. The demos work if I connect a 12V source, but connecting a USB cable doesn't power the board or enumerate with a computer. When connected only to USB, I can probe that power is getting to the OpenSDA MCU, but the main power busses are not on. Is my board just defective, or am I missing something obvious?