K-S2 Aperture block failure repaired Locked

KPM2 wrote:

Hello peterpainter

peterpainter wrote:

KPM2 wrote:

Hello flektogon

flektogon wrote:

KPM2 wrote:

Hello flectogon

In this link there is a nice description how it work:

https://www.pentaxforums.com/forums/151-pentax-k-30-k-50/321871-k-30-k-50-aperture-block-failue-repair-solution-available-3.html

Go to page 3 and read what IgorZ posted.

My two cents (I hope you say so) to this is:

This H -core what you see in the picture 4 of the OP, get permanent 'attracted' by the permanent magnet , therefor it be subject to a permanent magnetic alignment.

Even when you try a demagnetization, it would get quickly back a magnetisation via being permanent magnetic alignment in it's normal position. Therefore, I'm not sure if this problem has something to do with this.

Now the coils built up also a magnetic field, but it is revers to the magnetic field of the permanent magnet .... so that than both magnetic field sum up to a 'zero magnetic field'. This is the moment where the H-core can get draw out. This is done by the force of a spring.

I really think that in most cases this H-core simple jam and draw out therefore not quickly enough.

Have a look how this h-core get drawn out. It get draw out by the pin. In many pictures you can see that the alignment of the pin/H-core is not in the middle.

Now it's a little bit like you try to draw out a drawer:

no problem when you draw out it at it's centre knob.

but when this drawer has two knobs (one on the right side, one on the left side), your drawer jam quickly when you draw it out only at on knob.

Now because this pin is not aligned in the centre of the H-core, for me it's a little bit the situation above, it can jam.

Therefore some round the edge of this H-core. I personally would also try to spray it with Teflon.

But this is only my personal view and it is pure theoretical, because I have not such a camera and read only about what others described about this problem.

best regards KPM2

Hello KMP2,

Yes, I agree that the solenoid "getting stuck" problem is very unlikely caused by some residual magnetism. Yes, the solenoid (H-shaped core) has to be a permanent magnet, which is kept by some spring only partially immersed into the fixed armature/coil. When the coil gets activated (by a short electric pulse). the solenoid moves quickly in (if it doesn't get somehow stuck!). That pin which resides at the hole of the solenoid has to be the other side of the lever, which moves the aperture control lever of the lens. It is possible that this (body, not lens) lever causes some "side" force, which can have your mentioned "drawer closing" effect. Now it makes sense that filing off the sharp edges of the core could help. I would be then curious, what is the difference between this part and the original (Japanese) part used in the previous cameras. Maybe just better tolerance (smaller gaps between movable parts of the electromagnet).

I do not know what the difference is, but a better tolerance is a plausible cause to get no problems. I only read about this problem, because I once recommended my father a K500...and will be prepared to fix it when his camera get this problem. I did even read that not every camera has the same part. It looks like Pentax has more than one external suppliers for this part (I mean the H-shaped core). Maybe that's why you can not general say such a camera must get this problem, like the users itself post: some have still no problem, some do.

best regards KPM2

In the past I've come across posts where it happened after the camera has not been used for a while, and wondered if there was some commonality across failures.

In this post https://www.dpreview.com/forums/post/60341237 the aperture block performance was restored by a cycle of using the DOF preview function (on the RAW/fx button) a number of times plus test firing etc. although when this was posted on pentaxforums Adam said that a number of people had tried the same fix but the problem recurred later. Mmmm. Actually, it seems odd to me that the RAW/fx button should work with an aperture block failed camera, presumably the function operates using some different components etc......

I think this DOF-trick is great. When you use the DOF, this jammed H-shaped core has more time to move...and get eventually back in a un-jammed position. For test firing that would mean (to my mind) a longer shutter speed is better than a short one....for to let this jammed part time to move.

best regards KPM2

Yes, I like the method too, and thanks for the explanation. It's the sort of thing I would do years ago with old manual cameras that weren't functioning too well. I was disappointed that Adam said others had tried it and the problem recurred later. Don't remember seeing the method discussed on pentaxforums before, but I don't go there very often - too depressing reading the K30/K50 threads and I get the feeling that I should be 'donating' every time I'm there! However the process can always be repeated* if the problem comes back, annoying but better than abandoning the camera completely and as a leisure user it isn't critical for me that the camera functions every time.

My K50 hasn't been hit with the problem, but if (when?) it is I'll certainly use that approach.