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01-23-2011, 03:46 PM - 13 Likes   #1
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DIY SDM repair!

Good news everyone.. I just did a successfull repair on my defective SDM-focus DA* 16-50!

I recently got at tip about a blog post from [a certain banned user from this forum] that referred to another Chinese Pentax user on a forum thread who had successfully repaired his 16-50 with SDM failure. The repair is quite simple and consists of turning the back part of the SDM motor itself apparently to release it from a mechanical jam.

I admit, I din't have much belief in it, but decided to give it a go anyway. When the lens first failed (well over a year ago) I actually did dismantle it to check for errors myself, but I didn't dare to touch the small screw that seems to be glued on to the back part of the SDM motor. I assumed it was supposed to be a stationary item, and I didn't want to wreck it completely before sending it in for (the rather expensive) repair. OK, I didn't want to make a complete fool of myself to be honest. I did get a quote for repair abroad, and decided to put it on hold.

However, this Chinese guys success led me into giving the DIY attempt another go. The mechanics and plastic gears in the focusing part moved just fine with no apparent problems, just as it did the first time I opened the lens. I put a scredriver into the small screw head at the back of the motor and gave it a twist - and it moved slightly. The screw and the whole back part of the motor moves. It was really tight and not easy to turn, but I gave it a bit of massage back an forth before putting the lens together again. And, believe it or not - the lens focused again on my K-7! After well over a year just collecting dust and reminding me of really bad second hand deal, I now have a fully functioning DA* 16-50 again!!

Focusing now make a little bit of a squeeking noise, but the speed seems to be just as it was before it failed. I'm wondering if a bit of carefully added lubrication could make it even better and perhaps avoid it getting jammed again in the future. However I'm not sure exactly how the SDM motor is designed and I don't want to put lubrication onto parts that should not be exposed of it.

All in all I'm quite happy right now Having saved about 400 usd in repair costs, at least for now, and not having the dead DA* sitting on the shelf reminding me of a bad deal.. I wish I had dared fondling with the motor the first time I dismantled the lens though.


The original Chinese article can be found here (and google translate gives a nice chinglish mess of it): 在Wayli的启发下,我修理好了DA*16-50镜头SDM故障 - 无忌论坛

UPDATE: I've made a guide for this DIY repair online.


Last edited by sveinmb; 01-29-2011 at 03:01 PM. Reason: added link to online guide
01-23-2011, 03:51 PM   #2
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That sounds great! Got any pictures?
01-23-2011, 04:54 PM   #3
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Why post this without pictures?
01-23-2011, 05:55 PM   #4
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Here is the link.


Last edited by Blue; 11-24-2012 at 11:43 AM.
01-23-2011, 07:37 PM   #5
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lubrication

I would not lubricate the motor if I were you. Piezoelectric motors rely on having high friction between the rotor and the stator. Applying lubricant to the motor would compromise its operation.
01-24-2011, 03:54 AM   #6
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Sorry for not taking any pictures while I did this. I might consider dismantling it again tonight to create a full repair guide, but right now I'm just happy it's working

The photo at RH's blog show the SDM motor with its ribbon cable and the apparently glued screw head on top. (See the blue glue/epoxy/whatever around it) Notice that the gears both on top (in metal) and below (white plastic) did move just fine on my lens, but giving the motor itself some twisting through the back side screw head somehow made it work again.

The tap in the right circle on the picture is the af screw for cameras without SDM support, it's all connected through a series of metal and plastic gears.


Ayoh: just as I thought. That's why I didn't try any lubrication..

The next step will probably be to find a replacement oem motor that we can use in our lenses if a motor is beyond repair ? It wouldn't surprise me if it's actually a standard item that is not designed by Pentax from the ground up. For instance Shinsei Motor has some pretty similar designs in their lineup.
01-24-2011, 04:11 AM   #7
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Thanks for sharing this experience - just let us know how the lens fares with time as although I hope it is, it may not be a lasting solution.
01-24-2011, 04:43 AM   #8
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I'd be most interested in seeing how the screwdrive from the camera is coupled to the SDM/Lens AF system. Does the screwdrive turn when rotating the motor. Could it be that the camera motor adds some extra resistance that fries the SDM?

01-24-2011, 05:26 AM   #9
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Looks good

just a side note RH tip

3. Use a high quality cross-type screwdriver with matching size, with magnetised tip;

Just don't, take a magnet too close to those lens shutters and goodbye lens.

Use brass watchmakers with a trace of bluetack wrapped on the tip.
01-24-2011, 10:12 AM   #10
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QuoteOriginally posted by Ayoh Quote
I would not lubricate the motor if I were you. Piezoelectric motors rely on having high friction between the rotor and the stator. Applying lubricant to the motor would compromise its operation.
I'm not sure if that is a piezoelectric motor.

As I understand it, piezoelectric ring motors are usually ones that go around the circumference of the lens. This looks like it is nothing more than a small stepper (or similar) motor.

It's also proof that SDM is, in itself, not fundamentally flawed in terms of reliability - They probably just need to make some small tweaks to the tolerances of that motor, and in fact the problem may be fixed in newer lenses.

e.g. one of the components is flawed in manufacture, the design itself isn't fundamentally flawed. No need for a "SDM II", just use a different micromotor or fix the flaws with the existing one.
01-24-2011, 10:24 AM   #11
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QuoteOriginally posted by Entropy Quote
I'm not sure if that is a piezoelectric motor.

As I understand it, piezoelectric ring motors are usually ones that go around the circumference of the lens. This looks like it is nothing more than a small stepper (or similar) motor.

It's also proof that SDM is, in itself, not fundamentally flawed in terms of reliability - They probably just need to make some small tweaks to the tolerances of that motor, and in fact the problem may be fixed in newer lenses.

e.g. one of the components is flawed in manufacture, the design itself isn't fundamentally flawed. No need for a "SDM II", just use a different micromotor or fix the flaws with the existing one.
I don't think that would cut out considering it's lagging behind HSM.
01-24-2011, 09:20 PM   #12
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QuoteOriginally posted by sveinmb Quote
Notice that the gears both on top (in metal) and below (white plastic) did move just fine on my lens, but giving the motor itself some twisting through the back side screw head somehow made it work again.
Do you think you could have given the motor the required "massage" by turning the screwdrive slot on the lens? It just depends on whether the two are coupled with or without a clutch.

If one could turn the motor by turning the screwdrive slot then this would mean that a "revival" of the lens might be possible without opening the lens.

I reckon there are more severe cases of SDM failure in which your procedure won't work but it is very useful to know that one can at least attempt a DIY solution.

Thanks for sharing! (Not that I intend to get an SDM lens anytime soon... )
01-25-2011, 08:33 AM   #13
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Wow. This is good info to know! If my SDM goes out I'll be sure to give this a try! Of course, if there's still warranty left then doing such a procedure would void the warranty.

If the screwdrive is directly hooked up to the motor, then the resistance posed by the camera's af motor may be a problem. However, we need to confirm whether there is a clutch or not. Would it be possible to pull the screw drive part out of the lens and assemble the lens back together and see if there is any difference? I guess that would only help if the lens was tested after that for a long time...
01-25-2011, 08:34 AM   #14
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I wonder what percentage of 'broken lenses' could have been fixed by doing this?
01-25-2011, 08:42 AM   #15
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Hmmm might be picking up a da* now =]
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