2100 motors
I had the same problem with my Sadoun sg2100, one button motor.
I finally opened the case and found that some of the wires protruding from the circuit board were too long and were touching the divider (inside the cover) between the circuit board and the motor.
I clipped the wires and haven't had any problems with it since.
I recently examined a one-button version which had died (of other causes), and was aghast to see no insulator under the PC board.
If built and assembled properly, that -could- be okay in theory.
But, in practice, I'd never let it out the door!
Some damned manufacturing engineer probably got a gold star for saving half a penny per motor!
On a similar note, there are some moving wires inside the motor housing.
I think they go to the limit switches.
It's possible one of them broke (a poor design).
That might cause your problem.
And from inspection, it looked like they could be mangled by the mechanism, if they weren't located perfectly.
That could happen if ya opened the case, and didn't know exactly how to dress the wires before reassembly.