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Sigma 19mm F2.8 for Micro four thirds - typical voice coil repair
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I have a soft spot for the Sigma DN Art lenses. They offer great image quality, come in three versatile focal lengths (19mm, 30mm, and 60mm), and are incredibly compact. In a pancake-sized design, Sigma engineers have packed a very capable lens with excellent sharpness and pleasant rendering.
I also love this series for its very common, almost charmingly typical issues. These flaws show up just slightly less often than always - and are generally very easy to fix.
This time, the 19mm version (for the Panasonic/Olympus Micro 4/3 system) showed no signs of life other than some noise, and threw an error when mounted on a camera.
Let's tear it down (with pleasure) and see what's going on this time.
Even before opening it up, I already knew where to look - because there are exactly two common problem areas: the aperture mechanism and the focusing mechanism. To be fair, there are only two major parts in this lens, so you could say that "everything breaks" in it.
The Teardown
Like many Sigma lenses, this one is disassembled from both ends. First, remove the decorative ring around the front element - you'll absolutely need a lens spanner wrench for this step.
Underneath the ring, you'll find screws holding the lens hood mount. Remove those too.
Front lens can be left where it sits, but there is no harm to remove it:
Next, flip the lens over and unscrew literally everything in sight - the goal is to separate the mount connector, the bayonet, and the decorative rear insert from the main body.
Then unplug all ribbon cables and remove the main circuit board.
Now you have the optical block in hand. By unscrewing three screws on the bottom, you can split it into two halves.
The aperture assembly needs to be removed and inspected. I recommend immediately detaching the aperture motor and inspecting the gear under a microscope - a cracked gear is the first typical failure. In my case, everything was in great shape. (if not - see my other post: Sigma 19mm F2.8 aperture repair Manually moving the aperture blades felt smooth and easy throughout the entire range.
So, we dig deeper - down to the focusing lens. To get there, remove the closing magnets (they aren't glued in, just held by magnetic force, and they aren't polarized - you can put them back in any orientation), and unplug the coil ribbon cables.
And here's the culprit: one of the coils had completely detached from the focusing lens holder!
This is not a big surprise - it's a common issue in this lens series. The glue used to fix the coils is strong but brittle (likely a pigmented epoxy resin).
The repair is simple - reattach the coil with glue (T-7000 is my favorite), let it cure, and then reassemble the lens just like it was.
As expected, everything worked perfectly after the repair.
The only thing that puzzled me this time - every single screw showed light signs of previous screwdriver use. So someone had been in here before me. Why didn't they fix it? That's a mystery.
Wishing you great shots with great gear!
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Comments
Hi, did you ever come across a Sigma DN Art lens where the lens fails to initialise on camera startup? Have this problem with the 60mm Sony version. All you hear is a dampened squealing noise. Camera display only shows dashes instead of values. Fault is intermittent. 50% of camera startups go fine, 50% show the problem described above. I checked everything in the VCM twice. All out of ideas, maybe you got one.
I would check how does the aperture behave. It is visible from the front, and it might stuck as some position, hence error. I guess lens controls aperture position at _closed_ state, so if the aperture stucks open is the problem. Doubt VCM issue.
Already swapped the gear of the stepper motor, aperture opens and closes normally across the whole range. Blades move perfectly without the motor. Checked the photo interrupter in the aperture for dirt. Super weird case.
Just found out that the problem will never occur as long as the lens is pointed downwards. Must be some kind of strange VCM issue. Maybe the magnetic strip is damaged.
This unit is quite straightforward. Tighten the sensor, it has a shim under it. Then ensure that lens is moving freely, and release magnetic sensor if needed. That's basically the only adjustment needed
Interesting, did you already come across a case where removing one of the sensor shims fixed a startup issue?
Huh, I think I fixed it. Didn’t remove shims but I gave extra pressure on the metal retaining plate of the sensor while screwing in the two screws. Maybe the foam on the inside of the retaining plate contracts with age reducing the pressure on the sensor. Anyway, thank you for your replies!
Happy that it worked!