Hi everybody...
I got a k10 recently, low shutter count, great condition but the Auto Focus was intermittent at best and at worst just could not auto focus.
I regularly use Manual lenses so not having the AF work everytime was not a big big deal. When I did try out an AF lens, the lens would just go "back and forth" as if it could not see anything in front of it OR it would work sporadically. I tried cleaning OEM focusing screen etc, but still no joy. One day after a few weeks of not using any AF lens on the K10, I decided to try one out. Darn it, it worked like a charm with every AF lens I own, but then no more than 2 days later the AF went back to it's old self.
The only thing I could think would cause this were the contacts on the camera and/or lenses. I went ahead and aggressively cleaned the k10 contacts with lens cleaning fluid and a micro fiber cloth, slapped an AF lens on camera and it has not stopped working... In fact, it AF very well even in near darkness, I've tried every scenario and lighting condition I could think of and the auto focus just shines!!!
I've seen this "k10 will not auto focus" both here and on google, and I think cleaning the contacts on the camera as well as on the lenses is the answer... at least for me.
Hope this helps, thanks, Rick
Pentax-F 50/1.4