Originally posted by ohmic314 I think people are focusing on the plastic as a red herring.
This is not about thinking but about verifying. The red hering is often based on mixing up the most simple laws of physics:
Originally posted by ohmic314 I looked at the horseshoe part of the solenoid and found the green solenoids had a much flatter surface than the white solenoids.
How many green solenoids did you have for this comparison? You mentioned the single one from your K50.
Originally posted by ohmic314 This led me to believe that the cause of all the issues is this seemingly benign change they made to the solenoid part.
They did not make just one but many changes over the time being.
The green China-solenoid itself has been changed/modified three times. Your green solenoid is from the first manufacturing period.
Originally posted by ohmic314 For those of you that have taken physics, inductance is related to the gap in the magnetic path.
With all due respect but I don't think it is a good idea to claim to have taken physics and then right away mix physical laws upside down:
Inductance happens in electrical systems, i.e. coils! (and in our solenoid in those two coils as described later on)
The inductance is related to the winding of the coils and what material they are wound onto and what voltage is applied to the coils to induce inductance!
Originally posted by ohmic314 The larger the gap, the *less* the inductance.
That is total wrong: There is no inductance at all. Only magnetism by a permanent magnet!
Inductance we have ony then, when those two coils see applied voltage!
The larger the gap between the plunger from its counterpart, the *less* the magnetic holding force of the permanent magnet.
There is zero inductance!
Originally posted by ohmic314 In addition, a reduction in magnetic hold strength.
Again wrong of course: ONLY a reduction off magnetic holding force.
The magnetic strength stays the same, the magnet does not change.
Originally posted by ohmic314 If the junction between the horseshoe part of the solenoid and the magnetic side is slowly smoothed down
Also wrong:
Solenoids in Pentax-bodies usually fail after longer times of no use of the camera. Often with very low shuttercount just because they haven't been used (see attached pics!):
The plunger sits all this time close to the permanent magnet and the alloy which holds it which itself is magnetized. Thus the plunger is stronger magnetized, increasing the that one of the alloy-body. The release i.e. the time when the plunger moves away is very short: Depending on the given exposuretime!
Aside from this: Nothing is smoothed down, if heavy use the opposite happens: The surface does get sometimes a but rougher, because the plunger "slams down" onto the alloy-body!
I have observed this many times!
Originally posted by ohmic314 .....reducing the gap, the inductance increases
No, because there is zero inductance!
Originally posted by ohmic314 .... and the magnetic hold strength increases.
Of course it does. Thats the whole point and part of the design.
But the magnetic holding force decreases mainly because INDUCTANCE builts up in the two coils at that very moment when the 7.2 Volts/DC are applied to those two coils: To produce an exact defined opposite magnetic field to nullify that one from the permanent magnet. But this is only for that short time of exposure!
Originally posted by ohmic314 This is where the manufacturer messed up. They made the surface too flat and/or made the plating too weak, causing the gap to slowly decrease with time.
And you know this from inspecting this single green solenoid of yours?
Because the opposite is the case:
Since Dec.2015 the solenoids inserted into Pentax bodies (incl. the K50) have a flater surface which is shinier and since then we have
way way less failures!
Actually:
The surface of the white made in Japan solenoid is in most cases smoother and better manufactured as you can see
HERE:
Left the plunger made in Japan, right the plunger made in China. The same goes for the other parts of the body.
Anyway: Because the plunger hits pretty hard against its metal counterpart (and as mentioned, over time the surface does get rougher) and then you apply paint onto this surface, what will happen is that small bits of paint will end up in the camera body over time which anybody sensitly wants to avoid like hell!
Replacing the plunger of the green solenoid with the one from the white solenoid isn't a good solution either, it was tried and tested.
But I did the test again: I have right now about 15 green China-Solenoids here on my workbench and I have a few used and a few NOS (New Old Stock) Japan-Solenoids here:
Not in one single case does the holding force decrease! It remains the same.
But: As the Pentax is already disassembled, it makes sense to simply carry out the tried and tested repair.
The other causes why the China-Solenoid is inferior:
- PET vs. PTFE
- uneven or less well machined parts
- non-parallel bodies left and right, the plunger slides in and out and thus scratches on the PET if not parallel
- more gap between those bodies and the plunger:
Very clear to be seen
HERE and
HERE
Anyway, as you wrote, now the white solenoid is in your Pentax K50, from your donor camera another white one is left.
Your K50 is working again, that is fine, congratulations for that.
And yet: Your strangest claim:
Originally posted by ohmic314 - For those of you with a white solenoid, but are afraid of soldering, try just replacing the horseshoe portion,
I found on my testing the inductance followed the horseshoe part
This sounds to me as if you made something up here:
- First you give the reader the impression that you know about the laws of physics,
- Then you show that you don't know anything about them and mix up inductivity with magnetic force.
- But then you top all this by claiming you acutally measured inductance: There is no inductance that could be measured there.
The only induced inductance is on the coils when the voltage is applied for that tiny fraction of a second.
There is no inductance you can test when you follow the horseshoe/plunger!
when you claim:
Originally posted by ohmic314 I found on my testing the inductance followed the horseshoe part
Meaning you actually measured inductance there!
With an inductance meter?
How can inductance of those coils "follow" the plunger (horseshoe)?
The plunger moves within a fraction of a second (if the Pentax is set to a longer exposure time then the plunger is released for exactly that time, i.e. the voltage of 7.2V is applied 1/6 1/8 1/10 1/13 1/15 1/20 1/25 1/30 of a second to those 2 coils.
And the plunger is released and away from the magnet.
The only thing that "follows" is the plunger which follows the lever it sits on,
and reverse, it "follows" back towards the permanent magnet when there is no more voltage on the coils.
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Attached 5x Shuttercount-readings (2 x K50, 3 x K-S1): All had a stuck solenoid and got the white solenoid and as it is very obious:
All with very low shutter count, one K-S1 just 6!!!