K-S2 Aperture block failure repaired Locked

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 have already Teflon spray and a syringe from a apothecary at home, because I would try also to apply Teflon, with the help of the syringe, on this H-shaped core.

To the problem itself:

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