Any known problems with Edirol PCR-M30 and MIDI?

Just a quick question: I’ve got a MIDI keyboard (Edirol PCR-M30) which is powered via USB by my computer. Is it possible that MIDI keyboards don’t send signals though the MIDI-Port when there’s USB plugged in? My Shruthi doesn’t receive signals (No note symbol) but the Edirol display blinks when I press notes.
I already checked the Octocupler and the diode but everything seems OK there…


Korg Microkontrol doesn’t send MIDI when connected to USB.


I think caps are adequate here as I plugged some DC adapter I had lying aroung in my MIDI-Keyboard.