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05-26-2011, 06:20 AM   #1
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50-135mm SDm problem repaired locally

Hi guys. Like many others , I recently had the problem where my prized 50-135 lost the ability to auto focus. One day it worked well, the next time I picked it up, nothing.

I searched for a solution to the problem, other than just sending it to CRK or Pentax and found a DIY solution that seemed promising, but I'm a big clutz and the screws in a lens are tiny. (and I finally admitted to myself that that I am no longer superman, and there are things I simply should not do)

I knew that there was a camera repair man who lived close to me and worked from home, so I looked him up. Turned out he is only about a kilometer from me - happy days.

Lets see if he can repair the lens given the DIY tutorial I had found. My lens had no warranty, and I had very little to lose other than a small fee if he could do nothing about it. It had to be worth a try.

My repair man turned out to be a small Japanese man who had been formally trained in camera and lens repairs at one of the big two.

Long story short, after only a couple of days away in hospital and a very modest fee, I now have a fully functioning auto focus lens again.

If any of the Melbourne community have a problem with SDM lenses I suggest this may be an alternative way of getting them back into operation. If you want details, please send me a PM.

The repair man told me in japanenglish that the lens was 'poor design', 'not big enough screw' (he was referring to the screw that goes through the AF motor) ,'needs screw both sides, in opposition, so as to not bind'

It looks like the torque of the lens hunting back and forth causes the screw in the motor to over tighten and eventually stop the motor from turning.

i'm a happy camper and hope this provides some clues to the problem and also a low cost, speedy solution to SDM failures.

Cheers!

Wayne


Last edited by wizofoz; 05-26-2011 at 04:27 PM.
05-26-2011, 06:44 AM   #2
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Good to hear there still is private craftsmen around!

Your repair guy must be a lot more skilful than the whole German Pentax Service together, where I took my totally not working SDM 16-50mm last year. All I got from them (apart from the four weeks light-treatment), was a four word statement "could not see the problem".
05-26-2011, 08:48 AM   #3
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QuoteOriginally posted by wizofoz Quote
The repair man told me in japanenglish that the lens was 'poor design', 'not big enough screw' (he was referring to the screw that goes through the AF motor) ,'needs screw both sides, in opposition, so as to not bind'
I think this is the 1st time the actual cause was ever quoted. I wonder how he fixed the lens though if it was a design flaw.

Last edited by wlachan; 05-28-2011 at 10:24 AM.
05-26-2011, 08:54 AM   #4
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QuoteQuote:
The repair man told me in japanenglish that the lens was 'poor design', 'not big enough screw' (he was referring to the screw that goes through the AF motor) ,'needs screw both sides, in opposition, so as to not bind'

It looks like the torque of the lens hunting back and forth causes the screw in the motor to over tighten and eventually stop the motor from turning.
That actually makes perfect sense. I take it the motor wasn't burned out but Binding?

QuoteOriginally posted by wlachan Quote
I think this is the 1st time the actual cause was ever quoted. I wonder how he fixed the lens thought if it was a design flaw.
LockTite?



05-26-2011, 03:00 PM   #5
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no, the motor was not burned out. It seems from what I can gather from his broken English that there is a screw in the centre of the SDM motor. This screw tightens on the disc of the motor and prevents it turning. The cause seems to be the in-out, left right, turning of the screw during focusing.

He fixed the problem simply by re-adjusting the torque (tightness) of the screw. Not sure if he used locktite.

This may also explain why the lens suddenly stops working after brief periods of non-use. Changes in temperature could be causing the metals in the disc to change dimension ever so slightly and apply enough resistance to stop the motor from turning (this is pure speculation on my part)

Interesting
05-26-2011, 03:14 PM   #6
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Might be worth posting the info with a blurb in the aus pentax user group. And what he said makes perfect sense if it is indeed the way it works.
05-28-2011, 09:45 AM   #7
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His statement that the centre screw over tightens it's self makes sense, if you read this posting by "sveinmb"

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/130429-diy-sup...or-repair.html

DIY SDM repair v1.0

he refers to working the centre screw backwards and forwards, maybe that loosened the torque sufficiently to release unbind the motor.

Greg
05-30-2011, 09:07 PM   #8
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I suggest John at Shutterbox in Toorak Rd Hartwell.

06-03-2011, 03:11 PM   #9
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This is very interesting...
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