Mark T:
Ok - guess I never did look at the actual signal on the coils before. The motor is connected to the BED via a 4 pin DIN connector which goes to a breadboard in the box on a 4-pin JST connector. From there the leads go to the BED terminals via hookup wire.
With the system running, motor ONLY disconnecte, (Arduino Pro and BED powered with 12VDC - I see a CLEAN step signal on any of the coil pins.
Next I power off the supply, have the scope probe on one of the DIN pins (motor coil), re-plug the DIN/Motor connector and switch on the DC supply, the coil signal immediately shows the 2.5 khz signal. Is this because the motor coils are now completing the circuit from the BED? This is an "OK" situation? 
=Alan R.