The failure I experienced was one in which the manual focusing wouldn't even work when mounted on the camera body. It did not matter if the camera was turned on, had a battery in it, or anything...so long as it was mounted on the camera all the way.
Originally posted by Ubuntu_user Uh, are you sure that your camera's screw drive isn't giving resistance somehow?
It is my belief that the camera's screw drive was giving the slightist amount of pressure on the lens' screw drive mechanism. The reason I suspect this is because when I pressed the lens release button and still had the lens on the camera body, both the SDM and the MF worked just fine.
After finding this out I took a small screw driver and gave the lens mechanical AF system a slight turn, re-mounted the lens and everything worked as I would expect it to.
This was back in November. After I started this thread someone posted a link in another thread to this thread
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/130429-diy-sup...or-repair.html which basically describes how I "fixed" my SDM failure issue.
I'm not trying to say that this is everyone's issue. I'm just wondering how many people are seeing an issue with the SDM function and it turns out to be something like this?
The failure didn't happen just by me putting the lens on one day. I had it mounted and over the course of an hour or two of using it the function started to die by not allowing focusing past ~5 feet.
Sorry for the long winded reply.