They run sufficiently warm enough now that I put the fan back on them but am running them off the 5V USB with good results.
Can you explain where you took the 5V from? I mean, where did you attach the red cable on the PCB?
One pin on the USB connector will be supplied +5VDC from either the hub or the computer that your grid is plugged into. Thats what he's talking about. Not sure which pin, probably pin 1 or pin 4.