Fixing a seized AF motor
One theory on this is that the camera's software or settings may somehow be corrupted, so you should go through the process of resetting the camera to its original factory settings. If that does not clear up the problem, try another AF lens and conform whether the problem is the lens or the camera body. If the camera is not focusing another lens, then you may need to clean the contacts or look for some sort of damage.
If it turns out that it is the lens, the best solution is to send it to Tamron for service and see what they can do about it.
If you cannot send it to Tamron, you ought to see whether it is something as simple as some sort of internal dust or dirt collection blocking the mechanical switches and functions of the lens.
Start with making sure that you have a fully charged battery for the camera or AC power adapter for the camera. You do not want any of the problems with the camera to be related to having too little voltage available.
Make sure that the camera's power switch is switched off. You do not need to have the battery or adapter connected just yet.
Next, with the lens off of the camera, switch back and forth several times, firmly, between AF and MF and switch the vibration compensation off and on a few times. Of course, do not drop the lens. Also, unless you need the zoom ring locked, you may want to make sure that the zoom ring lock is fully off. While you are doing this, or after switching back and forth, check the electrical contacts on the lens and the camera body. If anything looks even a little less than shiny, clean the contacts.
With the camera's power still switched off, put the lens back on the camera.
Either put the battery in the camera or connect the AC adapter.
Set the lens to AF with vibration compensation off.
Switch the camera's power on.
Try getting the camera to automatically focus on something. If it works, turn the camera's power off, then switch vibration compensation on, then turn the camera's power on and try again. It may be fixed, at this point, which means that you can ignore the rest. Otherwise:
Turn the camera's power off again and switch to manual focus. Turn the camera's power back on and rotate the lens's focus ring (gently) all of the way through the focal range two or three times. Try taking one or two pictures, just to be sure that everything is working in manual. Turn the camera's power off and switch the vibration compensation, then turn the camera's power back on. Gently rotate the focus ring all of the way through the focal range two or three time, and then take two or three pictures to verify that everything is still working in manual.
After that, turn the camera's power off and switch back to AF with vibration compensation off. Turn the camera's power back on. Try to get the camera to automatically focus on something. If it works, then turn the camera's power off and switch vibration compensation back on again. The turn the camera's power on and try to get it to automatically focus on something.
If all of this works, than you should be okay with it as it is. You may still want to send the lens in to Tamron to get it serviced, in case the problem was some sort of lint or dirt getting caught up in the gears or servo that moves the lens through the focal range.
If it does not work, you could try to force the lens to re-engage the autofocus servo. It will probably void your warranty, if you still have one, so you are better off send it in to Tamron for service, first, before trying it. Also, as the manual and common sense would indicate, if you try to force the lens to adjust its focus ring while it is switched to AF, you could easily break the mechanism in the lens.
With that being said, some people claim that they got their lenses to return to proper autofocus by leaving the lens switched to AF and trying to rotate the focus ring manually. One person says not to "force" it, his just took a "firm push". I have not tried this, so I do not have advice on how much force may work or how much will damage the plastic bearings, gears and teeth inside the lens.
on May 05, 2014