jws,
On the cable, two pins are for DC Power and Ground, the other pin is for remote operation. The two pins farthest away from the 'key' tab are for power and ground.
I doubt what you are seeing is cable related, which tends to be.. will not work at all.
How old is the unit? My Premier lasted 7 years before biting the dust. At that time average lifespan was 5 to 7 years.
The newer S200 style robots look like they are only lasting 3 to 4 years and some less than that..
I am not sure if 27 VDC will power the unit, or not, but my gut says it will.
Thanks,
Jim R.