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01-31-2020, 07:15 AM   #376
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QuoteOriginally posted by cfrpcopy Quote
I just bought a "for parts" *ist D S as a donor camera to replace the failing solenoid on my K-S2. I took it apart and found one white solenoid for the flash lock, and one gray one for the aperture. I'm planning to use the white one in the transplant, both beacuse I figure the flash was used less than the aperture, and the listing for the source camera mentioned specifically that the aperture wasn't working. But I'm still wondering what this gray solenoid is.
Your thoughts about the white solenoid being less used is correct.

What really surprises me: The black solenoid from the aperture control has the red thread-locking laquer which indicates that either this solenoid was in your DS from new or it was replaced but then received the same laquer to fix the screws.

01-31-2020, 08:57 AM   #377
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It looks to me that the black/grey solenoid was a replacement part in the DS. Perhaps someone had tried to repair a fault. If you look at the left side hole in that solenoid, you can see the impression of a screw or something around that hole, an indication that it had once been mounted in another piece of equipment. There also is some red thread locker on that side of the solenoid.
01-31-2020, 06:55 PM   #378
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The left side (in the picture) is where the screw was that held it in the camera. I had to break the threadlocker to get it out. The threadlocker is also on the right side where it was just on a post, which seems weird to me.
07-20-2020, 02:19 PM - 1 Like   #379
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Thanks to the info found in this forum, I just fixed a K70 and a K50 last weekend (using a K20D and a K100 as white solenoid donors).

You can check the details of the service with photos here: ebuy05 Blog - Where new and old tech coexist: Pentax K70 DSLR (K50/K30) - Dark photos fix - Solenoid replacement

07-21-2020, 12:10 AM - 2 Likes   #380
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Well done with the repair.

In your Blog there are a few parts which I find are either critical or just wrong:

Critical:
- One should always use the Body mount cover for protection!
I like Pentax 31007 best, because it allows the front to come off without having to take the body cover mount off.
The cheaper transparent-white plastic version is larger and has to be taken off when one takes the front off, but at least it protects. Otherwise the danger for collecting dust/dirt/fluff is given which is not what we want, particular for the sensitiv AF-sensor region below the mirror!

- I just wouldn't give others the idea to use a filed green solenoid for the aperture in another body such as the K20D:
All too often those filed solenoids have failed after a while or worse: Brought havoc about!
Some now sell such modified bodies (but won't tell about the solenoid-swap). IMO this is cheating.
I came across used defunct Pentax bodies which I bought for their solenoids only to find that green solenoids have been built in.

Swapping the solenoid from the flash circuit of a *ist, K100D, K200D etc. is different because thats how Pentax started to test the green solenoid, it never failed there. But then: If one sells such a Pentax body, one should mention it because many buy used Pentax bodies for that very white solenoid.


With one comment you are wrong:

"Unfortunately, due to a failed cost savings attempt on Pentax' side, a cheaper aperture solenoid was used on their K30, K50 and K70 model cameras."

This was not the case and I have described this here:
A LITTLE BIT OF HISTORY: Development of the solenoid in Pentax cameras - PentaxForums.com
in all detail.

It was not a cheaper solenoid chosen by Pentax, it was the manufacturer Shinmei moving production from Japan to China!
There were no Japan solenoids available!

Also the solenoid in the K-70 as well in some other Pentax bodies has been modified and bettered, all Pentax bodies using a solenoid from Dec. 2015 onwards have it and there are way less failures, see:
Solenoid in Pentax K-70 - PentaxForums.com

One could possibly estimate that Pentax bodies manufactured pre-12/2015 had a failure-rate of 7%, maybe even 12% (this always will be a guess) but after 12/2015 it is within the usual standard less than 2%.


Of course there are those who deny it's the solenoid but that is just based on zero knowledge or evidence.

Last edited by photogem; 12-16-2020 at 12:23 AM.
07-21-2020, 09:05 PM - 2 Likes   #381
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QuoteOriginally posted by photogem Quote
Well done with the repair.

In your Blog there are a few parts which I find are either critical or just wrong:

Critical:
- One should always use the Body mount cover for protection
I like Pentax 31007 best, because it allows the front to come off without having to take the body cover mount off. The cheaper transparent-white plastic version is larger
and has to be taken off, but anyway, it gives the needed protection. Otherwise the danger for collecting dust/dirt/fluff is there and not nice, particular if falling into the AF-sensor region below the mirror!

- I just wouldn't give others the idea to use a filed solenoid for the aperture in another body such as the K20D:
All too often those filed solenoids failed after a while or brought havoc. Some now sell those bodies (but won't tell about the solenoid-swap). To me this then is cheating.
I came across used defunct Pentax bodies which I bought for their solenoids only to find that green solenoids have been built in.
Swapping the solenoid in the flash circuit of a *ist, K100D, K200D etc. is different because thats how Pentax started to test the green solenoid, it never failed there. But of one sells a Pentax body then, one should mention it because many buy used Pentax bodies for that very white solenoid.



With one comment you are wrong:

"Unfortunately, due to a failed cost savings attempt on Pentax' side, a cheaper aperture solenoid was used on their K30, K50 and K70 model cameras."

This was not the case and I have described this here:
A LITTLE BIT OF HISTORY: Development of the solenoid in Pentax cameras - PentaxForums.com
in all detail.


It was not a cheaper solenoid chosen by Pentax, it was the manufacturer Shinmei moving production from Japan to China! There were no Japan solenoid anymore available!


Also the solenoid in the K-70 as well in other Pentax bodies has been modified and bettered, all Pentax bodies using a solenoid from Dec. 2015 onwards have it and there are way less failures, see:
Solenoid in Pentax K-70 - PentaxForums.com

One could possibly estimate that Pentax bodies manufactured pre-12/2015 had a failure-rate of 7%, maybe even 12% (this always will be a guess) but after 12/2015 it is within the usual standard less than 2%.


Of course there are those who deny it's the solenoid but that is just based on zero knowledge or evidence.
Hello photogem,

Thank you for the valuable comments and deep knowledge shared on this matter. I must say your posts regarding this issue were important to me in order to learn about some of the tricks required to perform this fix.

I agree that everyone should use a body mount cover when handling a camera to avoid dirt or damages to the mirror/sensor (especially when handling an open camera). And of course, I do not encourage the sanding of the green solenoid. I just did this and installed it on the K20 as an experiment to myself as I no longer use this camera, even though I (still) find it a great one.

And indeed, I heard that the K70 have an improved green solenoid, but mine still failed. Perhaps I was unlucky?

I appreciate the corrections and updated my post accordingly: ebuy05 Blog - Where new and old tech coexist: Pentax K70 DSLR (K50/K30) - Dark photos fix - Solenoid replacement

Cheers!
11-09-2020, 07:30 AM   #382
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Thanks for the work you've done)
12-15-2020, 09:34 AM   #383
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A lot of food for thought as I think of the $359.00 K50 package I bought four years ago from MicroCenter The package came with both kit lenses, a 4Gb eye-fi HDSD card, an AF200FG Flash, and a Lowepro adventura 170 case that just fits everything.
My wife seldom uses it but so far everything works great.

12-15-2020, 09:45 AM   #384
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QuoteOriginally posted by EnglishBob Quote
My wife seldom uses it but so far everything works great.
Too keep danger at a minimum, just use it once a week at least. Few shots. It won't hurt but the opposite!
01-05-2021, 05:48 PM - 1 Like   #385
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Hi photogem et al. I can report another successful solenoid replacement in a K50. My camera was producing the 'dark images' described by many users here. Shutter count was ~1850 when it became too annoying to tolerate any longer. My donor camera is an istDS; I used the solenoid from the flash actuator, and put the green solenoid from the K50 in there. This was 3 years +3days ago; now I am at ~5040 shots, with no problems since. I was thrilled that it worked. My soldering skills are rudimentary, due to shaky fingers and poor closeup vision. But the camera was worthless without the repair, and now I can do my focus stacks. Thanks so much! John
01-06-2021, 01:37 AM   #386
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QuoteOriginally posted by JohnLivesey Quote
Hi photogem et al. I can report another successful solenoid replacement in a K50. My camera was producing the 'dark images' described by many users here. Shutter count was ~1850 when it became too annoying to tolerate any longer. My donor camera is an istDS; I used the solenoid from the flash actuator, and put the green solenoid from the K50 in there. This was 3 years + 3days ago; now I am at ~5040 shots, with no problems since. I was thrilled that it worked. My soldering skills are rudimentary, due to shaky fingers and poor closeup vision. But the camera was worthless without the repair, and now I can do my focus stacks. Thanks so much! John
Great work, particular as you overcame difficulties and just did it... and you did it well because inserting the green China-solenoid into the *istDS flash-circuitry is that bit more difficult. Often people lose that tiny plastic rod which acts as a switch when the pop-up flash closes.

Using the green China-Solenoid there makes sense because it was tested there in the K100D up to the K-r for almost 4 years and never made any difficulties.

Last edited by photogem; 01-06-2021 at 10:44 PM.
01-10-2021, 05:11 PM   #387
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Hi all - first off, great work with this solenoid fix. When my original K50 had this issue and I had it replaced under warranty, I knew it was just a matter of time before it would break again. It seems since then, you all have figured out what's going on. I replaced my solenoid and this is the feedback I have so far.

I think people are focusing on the plastic as a red herring. I looked at the horseshoe part of the solenoid and found the green solenoids had a much flatter surface than the white solenoids. This led me to believe that the cause of all the issues is this seemingly benign change they made to the solenoid part. For those of you that have taken physics, inductance is related to the gap in the magnetic path. The larger the gap, the *less* the inductance. In addition, a reduction in magnetic hold strength. If the junction between the horseshoe part of the solenoid and the magnetic side is slowly smoothed down, reducing the gap, the inductance increases and the magnetic hold strength increases. 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.

Through your testing, you have already found that the pull force needed to extract the green solenoids is higher than the white ones. You've also found that the release time is much longer. This is directly related to the gapping between the solenoid. Here's the experiment you can run - place a piece of paper/plastic cut to the right size so it stays in the hole but only creates a single layer gap in the solenoid. Replace the horseshoe portion. You'll find the inductance has decreased, the pull strength has been cut, and the release time reduced. This is what magnetic designers do when they are designing custom magnetics and I have tested this with the green solenoid.

Now that you've learned all this, what am I recommending?

- Replace the solenoid with the white ones - that's the most reliable way
- 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
- For those of you without a white solenoid, try adding a gap to the solenoid by inserting a single layer of plastic/paper into the solenoid holes. I'd suggest tape, but that has a way of shifting and leaving residue. Alternatively, one could paint a single layer of paint/superglue/epoxy at the end of the horseshoe. Choose a paint that will withstand thousands of impacts between two metal objects. Make sure this paint is non-magnetic because we're trying to create an additional gap with air or some non-magnetic material. We're only talking paper thin here. You might even want to use tissue paper as it's thinner than regular paper. This method is least destructive and can be undone
- For those that really want to try, put a notch at the end of the horseshoe. Alternatively, one could just sand the end so that it's no longer 90 degrees. This may not work very well depending on the properties of the ferrite material the horseshoe is made out of

Thanks to everyone in this forum. That's what I like about my Pentax - all you out there that realize it's not about the most shiny and newest in technology. It's about having a well built camera/lens that stands the test of time.

In the process of replacing my solenoid, I have some extra white solenoids (two came out of the camera I used as the donor). Does anyone here want one for $20? I'll only be shipping the solenoid and within the US (it gets too expensive to ship internationally).
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SM-G781U  Photo   
01-11-2021, 04:34 AM   #388
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QuoteOriginally posted by ohmic314 Quote
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:

QuoteOriginally posted by ohmic314 Quote
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.

QuoteOriginally posted by ohmic314 Quote
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.

QuoteOriginally posted by ohmic314 Quote
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!


QuoteOriginally posted by ohmic314 Quote
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!

QuoteOriginally posted by ohmic314 Quote
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.

QuoteOriginally posted by ohmic314 Quote
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!

QuoteOriginally posted by ohmic314 Quote
.....reducing the gap, the inductance increases
No, because there is zero inductance!

QuoteOriginally posted by ohmic314 Quote
.... 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!

QuoteOriginally posted by ohmic314 Quote
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:
QuoteOriginally posted by ohmic314 Quote
- 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:
QuoteOriginally posted by ohmic314 Quote
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.
-----------------


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!!!


Attached Images
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Last edited by photogem; 3 Days Ago at 10:02 PM. Reason: Further errors highlightened
01-25-2021, 11:26 PM   #389
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I decided to put my money where my mouth was and put a dab of car paint on my green solenoid. Just as I suspected, my camera works perfectly now with the old solenoid. I guess that means I have two white solenoids I can sell now.

I am not here to make money or try to force anything down someone's throat. I thought I just offered some advice based on science and measurements. I figured some people don't have a lot of money to spend or don't know how to solder, so I offered some suggestions that might work. Non-destructive advice that can be undone.

Last edited by MarkJerling; 01-26-2021 at 02:13 PM. Reason: Personal attack part of post removed.
01-26-2021, 08:06 PM   #390
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QuoteOriginally posted by ohmic314 Quote
I decided to put my money where my mouth was and put a dab of car paint on my green solenoid. Just as I suspected, my camera works perfectly now with the old solenoid. I guess that means I have two white solenoids I can sell now.

I am not here to make money or try to force anything down someone's throat. I thought I just offered some advice based on science and measurements. I figured some people don't have a lot of money to spend or don't know how to solder, so I offered some suggestions that might work. Non-destructive advice that can be undone.
My experience with the green solenoid is similar. I didn't sand the flat ends or sides of mine down, but just the very corners of the ends very slightly, reducing the contact area by a tiny amount. It worked perfectly after that. My only hesitation with car paint would be that it will crush and flake over time.
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