Watched this happen years ago at OAK. The Hobart GPU was connected to a DC6 and the Captain tried (for reasons unknown) to turn over all four engines at the same time.
The Hobart jumped about three feet into the air, turned turtle and burned.
The Chief Pilot was not amused....and neither was the DirMaintenance.
Learned much later that the Captains previous paycheck bounced higher than a kite.