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Forum: Pentax DSLR Discussion 10-14-2016, 04:29 AM  
Fix for the aperture motor failure?
Posted By Shephard
Replies: 51
Views: 26,214
I would like to share my experience, it seems I successfully managed to fix the aperture problem on my K-30. And I discovered later a Russian forum talking about the same electronic part...
Anyway, the aperture controller mechanism is composed of several parts, including some kind of brake. This braking system didn't trigger in my case, causing the aperture blades to close all the way down at the few firsts activations. At first, I had to warm it up with 3 to 4 activations, then 5 to 6 a few months later, then about ten and then... I got bored, and took my screwdrivers !



Next to this double coiled electromagnetic brake trigger, are the aperture gears.
The way it works is not that difficult to understand when you can watch it by activating depth of field preview.

Here are the main steps :

- The gears are by some actuator.

-- So, the aperture lever translates.
-- So, the slotted encoding wheel turns.
-- So, the camera can count the number of slots passing through an optical sensor.

- When the required translation is achieved, those gears need to be stopped.

- The camera sends a current pulse in the brake trigger coils.

- The pulse releases the metal part (drawn in blue) from the attraction of the magnet.

-- So, the brake lever gets down.
-- So, the gears get stopped.
-- So, aperture is controlled !



The problem in my case, was the metal part not willing to leave the magnet's attraction. The gears were still working, the brake lever too. The pulse of current was also sent. So, I came up with the idea to slightly increase the distance between the magnet and the metal part by applying a thin layer of tin with a soldering iron (actually, it was more of a big drop that I thinned to the desired thickness afterwards). Logically, any non-magnetic material should do the trick !



After two times (the first one was two thick), it made my aperture controller working again !
The best part in this fix, is that the coils can be accessed just by removing the plastic covers. No need to recalibrate anything !

I hope this post will help you !
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