Originally posted by Brooke Meyer Like Norm said, some us have never had trouble. My 2009 vintage 50-135 has been on 7 different K bodies, made hundreds of thousands exposures and is still my preferred portrait lens. My 17-70 was bought used about 5. years ago and is also heavily used. Never an issue with either.
This has always been the issue. If there is a magic return percentage that triggers a recall, then the SDM lenses never reached it. How many lenses are Pentax prepared to repair needlessly to cover a few that fail.
At the time I felt that there was a tolerance issue. To a perfectly spec'd lens there was probably never an issue. A barrel that was a little tight inside a tube causing more than the anticipated friction was burning out the motors in lenses that were harder to rotate than the spec. would predict, and the motor wasn't designed for anything but straight up spec. So if tolerances went your way and the focusing mechanism was to spec or loose, you didn't have an SDM problem. In the case where the out side tube was a little under spec (but still within acceptable tolerances) and the inside was within spec but the tolerances were a little over, those lenses died. Eventually they just put in a circuit board that produced a bit more current and for many (but not all) lenses it solved the problem.
It was a design flaw for sure, and most Pentax users are appalled at the way it was handled, but as far as I know it's ancient history.