K-S2 Aperture block failure repaired Locked

flektogon wrote:

flektogon wrote:

flektogon wrote:

DAVID MANZE wrote:

Firstly, well done!

Going back to my sound recording days, a build up of residual magnetisation was a common problem on audio tape recording heads, it caused a background grumble and other. It was routine to demagnetize the heads with an iron cored copper wound coil with an AC current which would "shake" the molecules around until their pole orientation was neutral.

From what I read here maybe the problem could also be cured by demagnetizing the offending core piece, it's a shame that many bodies find their way to the dumpster because of it!

Dave,

Actually that's an excellent idea, which could be even implemented by an addition to the camera F/W. Just like dust removal, or other "maintenance" setting, there could be the "demagnetization" setting, where this solenoid would be driven by an AC current with a slowly decaying amplitude. Well, the lens probably would need to be removed during such procedure, but within a second or two the core would be completely free of any residual magnetism.

I've got another idea. Because those failing cameras have plastic bodies, it might be possible to demagnetize this solenoid core from outside, just circling a suitable demagnetization tool as close as possible above this solenoid. Once I made such a tool for exactly what you mentioned, for the tape recording heads. It was a simple coil for 120V, but I drove it from the 220V AC power outlet (just for a short time) and as the core I used, well now I do not remember what kind of iron/steel rode it was, but some ferromagnetic material with the minimal residual magnetism. The rod protruded from the coils around 10cm. I have successfully demagnetized the audio tape recorder heads in all households along the entire street where we used to live .

So, do we have a skilled electro-technician around here, who have access to suitable material and could build such a tool? Well, it should be verified that it works, and if yes, such a tool can be "circled" around all unfortunate Pentax owners.

And my third (last ?) contribution to this problem: If this solenoid core/plunger can't be demagnetized from outside (circling with the demagnetization tool around the plastic body), it might be demagnetized through the aperture control lever, which is accessible when you remove lens, as this lever directly moves the aperture lever on the lens. This (body, not lens) lever is visible as a shaft inserted to the hole of the plunger, as OP shows in his pictures. Hopefully this lever is made from ferromagnetic material as well. Certainly there are ways how to beat even the least caring manufacturer.

One of the problems will be that, the two coils look to be wound with very fine wire with many hundreds of turns, any varying magnetic field will of course induce a voltage across the coil, possibly many hundreds of volts, very likely enough to destroy surrounding components.

It's also very likely in this situation to have a diode across the coils, eliminating the back EMF reverse voltage spike as the magnetic field collapses, this could cause havoc with an AC changing magnetic field. So there would have to be some way to isolate the coils, already things are getting complicated.

I can't see a way in which avoiding disassembly would be possible here, it's best to demagnetize and clean the iron "H" piece independently. It doesn't look the most impossible of jobs and someone brave enough to make a utube video showing the procedure could go a long way to help.

Dave's clichés