Originally posted by LeDave
3/5/2016 Update:
Hey guys, I found another cheap way to quick fix the SDM problem. You just hold the AF button down for a couple of seconds and let go, then you hold the AF button down for a couple of seconds and let go, repeat, repeat, and repeat until it starts to move and focus again.
Just three days ago I revived my seemingly defunct 16-50 AF using this method. Yesterday it needed revived again, but it didn't take quite as long to respond. This morning it again needed some coaxing to function normally, but not as much as the day before. I will continue this for the next couple of weeks, but if it doesn't soon start responding first time, every time as it is supposed to I will be sending it off to Uncle Vanya for a conversion.
I have had this lens since November 2012 and had the SDM repaired under a Square Trade warranty just a few months after the original Pentax warranty ran out. I am just getting tired of dealing with it.