Since Pentax made the SDM AF motor, the SDMs in various DA* lenses have been reported death by different users from time to time. In fact, such reports have never stopped. Recently, the death reports of SDMs have been about the DA 17-70. Examples:-
http://forums.dpreview.com/forums/readflat.asp?forum=1036&thread=33624008
http://www.dchome.net/viewthread.php?tid=778328
(Post in Traditional Chinese, or read the Google Translation Here)
So, the poor reliability of the SDMs really upset so many users and also put off quite some potential buyers as well, like what this guy tells. I think unless Pentax "improve" (actually debug) their SDM design to make it works more reliably (not even to mention to make it run faster), nobody would trust the SDM! (yet an example)
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Saturday, November 07, 2009
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Comments by IntenseDebate
SDM Issue Strikes Again - This Time DA 17-70
2009-11-07T22:09:00+08:00
RiceHigh
Issues|Lenses|Quality Issues|SDM|System Performance|System Reliability|
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potential · 800 weeks ago
Vytautas · 800 weeks ago
Raphael · 800 weeks ago
Read the original post in dpreview ;-)
Just a bit cleaning of the pins, and it now works "as new"
Bob · 773 weeks ago
Raphael, the fact that the SDM "comes to life" after cleaning is very often a false hope. The problem with SDM is typically intermittent. What brings the SDM "back to life" is often just the act of removing and replacing the lens. It has nothing to do with the contacts. It will probably fail again. Many people have "brought thier SDM back to life" after spinning the zoom rings and focusing rings, but eventually it fails again.