A Hong Kong DA*50-135 lens owner found that his lens always mis-focused in the range between 80mm to 135mm, so he decided to disassemble it and saw if he could repair it..
See:-
http://www.facebook.com/album.php?aid=268652&id=755984264&l=23d0a5f29b
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After the disassembly, he found that the electronic contacts in a metal brush form, which is part of the zooming mechanism, was distorted and thus causing bad contact, which should be the evil for causing the AF issue. He then reshaped the brush and then reassembled the whole lens, now everything is working normally! Brilliant, guy! You're really a great repair technician yourself! :-D My hat off! Possibly the local Pentax service centre couldn't trouble-shoot this problem for you straight-forwardly! :-( So, DIY is always great, provided that you know what to do yourself! :-)
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http://www.facebook.com/photo.php?pid=5707657&id=755984264&l=23d0a5f29b
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