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12-12-2015, 04:56 AM   #1
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DA* 16-50 SDM quick fix/check

After 1-2 months of inactivity, I did not use my DA* 16-50mm 2.8 for a while. When I mount the lens to my K5, the SDM was not responsive and autofocus did not work at all. As I'm aware of the motor issue for inactive lens, I thought "at last, SDM's dead".

Before I send it to repair or perform DIY repair, I thought I should keep on trying to engage the auto focus. So I did the following:
  • half press shutter button for many time, with varying durations (1-10 secs)
  • full press AF button at the back with varying duration, and on one very long press (~20 sec) the SDM kicked in again!
This is just to let you 16-50 owners know before you decide that the motor is dead. And I guess the best way to maintain the motor is to keep on using the lens...

12-12-2015, 05:11 AM   #2
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I think someone reported this is a capacitor in the lens not holding its charge.

So, yes, after a while of trying to focus it picks up enough charge from the camera's battery.

Not really related to the seizing up of the SDM motor, though.
12-12-2015, 09:33 AM   #3
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QuoteOriginally posted by clackers Quote
I think someone reported this is a capacitor in the lens not holding its charge.
Maybe Pentax should sell a trickle charger for their lenses...
12-12-2015, 03:31 PM   #4
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An electric motor does not go dead after a couple of months of no use,the culprit is most likely the quick shift clutch not letting go of the focusing mechanisms parts,and it won't let go until you move those parts manually.

12-14-2015, 05:32 AM   #5
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QuoteOriginally posted by BCtoad Quote
An electric motor does not go dead after a couple of months of no use,the culprit is most likely the quick shift clutch not letting go of the focusing mechanisms parts,and it won't let go until you move those parts manually.
I did rotate the focus ring manually many times while I was trying the method above.
12-14-2015, 11:41 AM   #6
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QuoteOriginally posted by mythguy9 Quote
I did rotate the focus ring manually many times while I was trying the method above.
I know this sounds lame but make sure that contacts on the lens and camera body are clean, and if you are using a grip the contacts for the battery inside the grip and the battery are dirty clean them with an eraser. I had some weird focusing issues with my 60-250,weird out of focus shots yet the battery said it was full, took the trusty eraser and did the contacts on the battery and the contacts in the grip now everything is A OK
Use a new pencil eraser much easier to work with also do the camera body the same way, the battery may look great but acids form a film on the metal without looking grungy give it a rub and give it a try good luck.
03-27-2016, 02:45 PM   #7
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QuoteOriginally posted by BCtoad Quote
An electric motor does not go dead after a couple of months of no use,the culprit is most likely the quick shift clutch not letting go of the focusing mechanisms parts,and it won't let go until you move those parts manually.
My lens is 2 years old, lightly used, I found similar problem with my copy today. Autofocus wouldn't work propely. I noticed that rotating focus ring wouldn't always move focus scale. I then switched body to manual focus and then focus ring started working like it should. Switched body back to AF and same problem again.

I took the lens off and with small screwdriver I tried to rotate screw drive in the lens. This was initially quite gritty. After few turns going backwards and forwards it would became nice and smooth in operation. There must be a clutch between screwdrive and SDM motor. This was obviously getting tight and therefore SDM was trying to rotate the motor in body (that is why switching body to manual helped, because it physically moves screwdrive shaft). Anyway my lens is back on camera and no problems since.
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