[reeftool]

While I don't own of these lenses, being a professional mechanic, I just had to check it out. A very well done set of repair instructions. Thanks Sveinvb for going through the work to provide us with this information. Sooner or later, I'll own one and this will likely come in handy.

[twitch]

The interesting thing about this is that SDM failures aren't caused by faulty motors themselves, but seemingly by the mechanics between the motor and focus mechanism becoming sticky or jammed.

So replacing a motor only solves the symtom not the cause. This explains why some get multiple SDM failures and motor replacements.

So talk of improved motors solving the problem is plain wrong, unless the new motor is so strong that it can unjam the jammed mechanicals.

[calicojack]

I notice that Pentax is now using the description "DC" motor. Is this just a terminology change or a design change?

[ytterbium]

Now this solution might change my mind about SDM lenses. Great. I wonder how hart it would be to stick simple DC motor / stepper in place of SDM. Probably some control problems and unexpected inertia.
Yet it seems to be connected only by two wires. Most likely AC power, if its a piezzo drive.

Because of the glue, the screw seems to be some kind of trim/adjustment.

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Last edited by ytterbium; 02-14-2011 at 06:09 AM.

[Ubuntu_user]

I notice that Pentax is now using the description "DC" motor. Is this just a terminology change or a design change?

I heard somewhere here on the forums that "DC" will be put in all upcoming DA zoom lenses while "SDM" will only be in the DA* lenses. Of course, this most likely is just a difference in names while the actual thing I would guess will be the same... I can't confirm that last statement though at this time, so take it for it's face value.

[Tom S.]

Now this solution might change my mind about SDM lenses. Great. I wonder how hart it would be to stick simple DC motor / stepper in place of SDM. Probably some control problems and unexpected inertia.
Yet it seems to be connected only by two wires. Most likely AC power, if its a piezzo drive.

Because of the glue, the screw seems to be some kind of trim/adjustment.

I would be totally amazed if the motors were anything but dc. DC motors can be reversed by switching polarity, plus the camera's electrics all operate from dc voltage. AC? Not likely.

[Entropy]

I would be totally amazed if the motors were anything but dc. DC motors can be reversed by switching polarity, plus the camera's electrics all operate from dc voltage. AC? Not likely.

All motors need AC. It's just a matter of whether the motor has built-in commutation (brushless commutation or brushes) or not - ones with internal commutation appear as "DC" motors.

Ultrasonic ring motors rely in an ultrasonic waveform being generated - def. not DC. The SDM micromotors don't seem to fit in this category. If anything they look like small stepper motors.

[Frogfish]

rep +1 for Sveinvb.

Great guide. Thanks !

[Tom S.]

All motors need AC. It's just a matter of whether the motor has built-in commutation (brushless commutation or brushes) or not - ones with internal commutation appear as "DC" motors.

Ultrasonic ring motors rely in an ultrasonic waveform being generated - def. not DC. The SDM micromotors don't seem to fit in this category. If anything they look like small stepper motors.

Perhaps you can explain that one to me. There are numerous motors that run strictly on dc current, and to my (limited) knowledge, cameras all use dc power. I know you can use an inverter to change dc to ac, but how practical is that? Unless you are saying that the brushes/commutator of a dc motor effectively change the dc into ac because it is reversing the polarity in the windings. In my book, this still remains a dc motor since it requires dc voltage to operate. My electric motor knowledge is based on learning's from many years ago, so maybe I need updating!

[calicojack]

Perhaps you can explain that one to me.

I also wanted to chime in on that "All motors need AC" statement, but I thought well maybe the newest technology....... I used to work on machines that were run on DC motors (big ones like 5-20 HP).

[Entropy]

Perhaps you can explain that one to me. There are numerous motors that run strictly on dc current, and to my (limited) knowledge, cameras all use dc power. I know you can use an inverter to change dc to ac, but how practical is that? Unless you are saying that the brushes/commutator of a dc motor effectively change the dc into ac because it is reversing the polarity in the windings. In my book, this still remains a dc motor since it requires dc voltage to operate. My electric motor knowledge is based on learning's from many years ago, so maybe I need updating!

That's exactly what I'm saying - a DC motor is just an AC motor with internal commutation (whether brushless due to integrated electronics, or due to brushes).

Having control over the commutation can give a system much greater precision than a system that uses a motor with internal commutation. If you look at the photos of the SDM system, there are at least four wires going to the motor in that flat cable - it's either a small ultrasonic motor, or a small stepper motor. My money is on it being a stepper, I'm fairly certain to have good torque ultrasonic motors need to be larger ring motors. The DC lenses probably just have a brushless DC motor (e.g. motor with internal commutation) that gets PWMed to make it rotate at a desired speed - Likely cheaper and faster but not as precise.

[sewebster]

There is probably something with direct current in these new DC lenses, but I wouldn't read too much into it, they're just using it as a marketing term.

[flash_xx]

Well, I tried it today on my 16-50 and it didn't work. I opened the lens several times to repeat the procedure to no avail. The first time I rotated the screw it was really stuck, so maybe the motor seized. As it stands I guess I'll have to send it in for repair, not much fun using manual focus.

It's not really hard to open the lens if you follow the guide, just be careful and remember, if you need to apply force you're doing it wrong.

[Particle]

Thank you VERY MUCH for this guide. I have waited for this a long time. Because I did not want to go the risk of opening the lens without at least some chance of knowing how to do this and whether this may help out.

Achtually I registered now here because of this guide. In order to express my thankfulness to the thread opener as well as all people involved in making this information/knowledge public!

I have had my 16-50 for two years now and did not use it for almost one year. My SDM was stuck. I opened the lens. As flash_xx states, I felt that my motor was really stuck. I made it moveable again, but after reassembling the lens, the SDM-AF still does not work.

Does anyone know where to get a spare part of that piece for a good price? Preferably in Germany or Europe, but overseas also possible.

Or does anyone have any further idea (dismounting the motor and disassembling the motor itself)? Does anyone know how to proof-check that it's really the motor?

kind regards,
Particle

[OldPentaxian]

The following tip may not work for all, but it has helped me twice over a period of time:
Mount the SDM lens (e.g., 16-50mm) on an autofocus body which has no SDM-compatible contacts, e.g. the ZX-/MZ-7. Activate the screw-driven autofocus and allow the camera to focus the lens several times over a wide distance range. Obviously this tip can only work with DA* lenses which support both screw-driven AF and SDM.
In my case, this seemed to "un-jam" the SDM (and jammed manual focus override) when I returned it to the Kaf3-compatible body mount (K20D). I've never had to have my SDM lens serviced.