[photogem]

I think the approach of Sergio Gonzales was worth trying out.
A lot of thought behind it and well researched.
But there are those hazards mentioned.

The problem is also that all half-baken solutions which cost almost nothing produce another problem:
People who have bad Pentax cameras can bring them to work and then sell them on ebay saying all is well.
This happened before, I know of a few who later had either the same problem again (and luckily could solve it by applying the Japan-Solenoid)

but some had a write-off. So I hope writing this won't serve the wrong way!


The main factors one has to deal with the China solenoid:


The magnet itself which is stronger! Magnetism does occur only when the plunger sits inside the magnetic body, i.e. close to the magnet.
But then the plunger of the China solenoid does magnetise stronger because one can say for sure, that the tiny but strong rare earth magnet does not gain strength.
When the camera is not used or in M-Mode, the solenoid is not in use, i.e . the plunger magnetises.


Many have tried using new Li-Ion orig. batteries, this didn't change anything.

Only Eneloops help for a while due to stronger surge-power.


The differences:
Switching time:
- The Japanese solenoid does need 2ms at 7,13V/DC to switch
- Chinese solenoid: 10ms!


Pulling force necessary to release the plunger:

- Japan solenoid: 1,2N
- China solenoid: 1,5N


I see it like this:
A good white solenoid is easy to find. With a bit of patience one finds one of the DLSR bodies mentioned and has 2 of them.
None ever failed.

Why risk further damage or total exodus if one can do it well?

[sergiogonzalez]

Dear Photogem:
A real pleasure to talk to you and exchange ideas! I must thank you and congratulate you on the beautiful reports on the history and quality of the solenoids. These reports made it possible for me to fully understand the problem of the solenoid. I don't understand how Ricoh hasn't taken precautions on this very common failure.
It is not in question that the best solution is to replace the green solenoid with one of Japanese origin (white). It's the best solution.
The problem is that, in places like Argentina, we are a long way from the big Pentax markets, which is why it makes us very complicated and expensive to get these types of spare parts. There are almost no Pentax disused cameras in this market. That's why I set out to investigate how to try to make the green solenoid walk consistently and safely, without intervening in its geometry and components.
Initially research with Teflon-based lubricants, but it was a failure as I explained in another thread. But by chance I saw a glass of graphite on my workbench and thought of solid lubrication. Make it work from one solenoid, after failure with other lubricants.
Now let's move on to certain considerations about graphite. As you say it is used for the manufacture of brushes of powerful and fast universal motors (with collector). This is no coincidence. Graphite apart from being a large electric conductor is the one that shows the least coefficient of friction that rotates at impressively large tangential speeds. This means that you have to provide graphite (brush wear) that is gathered in powder inside the motor cavities. This does not affect the operation of the engine at all, as this is planned and is maintained every time the brushes are worn.
But this app is not comparable with including graphite in the solenoid. For we will proceed has done a treatment with graphite for a single time to the inner surface of the reel and to the rubbing surface of the Plunguer and in such a small amount so that the graphite has to be inserted into the microstructure of the PET of the reel and the material of l Plunguer. (Sorry if I don't explain this in detail in another post)
Put by comparison, it's like when we write with a graphite pencil on paper. Graphite is introduced into the paper microstructure and remains there for a long time, can even withstand large frictions on the paper even liquids and remain in the microstructure. Broadly speaking, this is the concept of solid lubrication, widely used in state-of-the-art machines, including in the aerospace industry, introducing graphite, molybdenum sulfide or hexagonal boron nitride, also called white graphite.
We will not delve into the subject of solid lubrication, because whoever wants to do it there are fascinating internet posts about this system.
As for how to apply graphite to the solenoid so that the virus effect you mention does not occur, the following should be done:
1) Disassemble the solenoid, without disassembling the magnet holder.
2) Disassemble the magnet, marking its position to preserve its magnetic polarity.
3)Include a very small amount of graphite (equivalent to 0.5 m2) inside each reel of the reels. Or the tip of a 0.5 mm wide flat screwdriver)
4) With the Plunguer insert and remove it from the reels several times by pressing on all contact surfaces between the PET and the Plunguer. This action will cause graphite to be introduced into the macro and microstructure of the PET
5) Once operation 4 is complete, extract the traces of graphite from the reel cavities with compressed air at low pressure. (with the use of a cleaning pear is sufficient)
6) Place a small amount of graphite on a piece of paper propped on a glass and forcefully scrub the Plunguer against the graphite so as to insert it into its structure.
7)Blow the Plunguer to remove traces of graphite powder.
8) Treated the two pieces, reels and Plunguer.
9) assemble the solenoid using tweezers (do not touch the Plunguer with your fingers after treatment. Mount the solenoid in the camera.
As for the Diamagnetic property of graphite, I have tested with a magnet equal to the one that mounts the solenoid, and the magnetic flux of the magnet is not able to levitate even the smallest of the graphite grains. Diamagnetism is so small that it presents no problems. Moreover when the coil is unexciting (without applied current) the magnetic circuit of the magnet is closed and the traces of graphite (if any) will tend to stick to the PET of the reels. When the coil is excited, it cancels the magnetic flow of the magnet and the graphite should travel to the place that has the least magnetic flux, which is the gap between the magnet holder and the Plunguer. So the free graphite (if any) would always remain inside the solenoid.
I have checked the inside of my KS2 and can assure you that no contamination has occurred, and it has been in use for more than three months, and has not presented any diaphragm failure and in any mechanism inside the cavity where it is mounted on solenoid.
In the spirit of helping the community and being able to solve this problem in a very simple and cost-effective way.
Best Regards

[photogem]

Sergio,
It is a worthwhile approach and I understand that if there is zero graphite dust anymore inside the solenoid itself,
but the graphite is "rubbed in into the PET" there is no danger anymore regarding dust.


I have 2 x K500 cameras here, one my own with white solenoid and one which is from another person to be repaired.
I shall try your suggestion, it is easy.


My guess is that it will increase the bearing quality, i.e. the green PET body which is worn out will have less friction.
This could change the release time.
But what it won't change is the holding force, because this is due to the strength of the magnet.
This is why people retreated to filing/sanding/soldering, those methods do weaken the holding force but the plunger is going to move
move uneven.

Anyway, it has to be verified.

Why would the direction of a permanent magnet matter inside the magnetic body of the solenoid?

[sergiogonzalez]

Dear Photogem:
It is a good decision to try.
After you verify that it´s doing well, you'll be calmer.
Make sure that the Mirrors of the Plunguer are as bright as possible. Charge them into the water with a 600 grain sandpaper and then treat the mirrors with graphite as vigorously as possible. This will protect it from oxidation and better form solid lubrication and allow the Plunguer to be better retained and more quickly released.
You'll see how they improve the mechanical and magnetic characteristics of the solenoid. It becomes a reliable solenoid.
As for the polarity of the magnet is simple. You must respect the magnetic polarity of the magnet that is in accordance with the electrical polarity of the solenoid connection.
If any of these polarities were reversed, the solenoid instead of releasing the Plunguer would trap it and the mechanical logic of the non-functioning camera. That's the reason.
Keep me posted on your tests.
Best Regards

[photogem]

Longer time ago I had some solenoids with opposite polarisation and slightly different holding force.
When then the solenoid actuated, the plunger was pulled even further in instead of releasing.

I had tried to change the magnets orientation which I thought myself would do the trick but it didn't help!
Only changing the wires plus to minus and minus to plus did it. So I wonder what I might have missed there.



I don't have those solenoids anymore so I cannot do the same test.

With all logic it should be as you describe it.

[photogem]

I treated a green solenoid which came from an officially repaired Pentax K30.

This solenoid had failed again and I installed a white Japan solenoid inside this K30, it works very well now.


So I treated this green solenoid with graphited and installed it into a K100D which I have at the moment open for several tests.
The treatment was done as you suggested and I am quite sure that this way no contamination is going to be a problem, one can see that the green PET does change to a darker blackish colour, the PET takes the graphite-dust in. I then cleaned it very well: I used a strong vacuumcleaner, held the solenoid into the hose. Afterwards I cleaned it with compressed air. The plunger was treated first with
the graphite-powder on papter but I felt it would not do much. So I used a graphite pen and rubbed it and afterwards cleaned with the vacuumcleaner hose and then compressed air (which wasn't really necessary). So no daubt, there is no danger of graphite inside the camera!


As you probably know, normally the K100D is equipped with the white made in Japan solenoid.
I have tested filed/sanded and unsanded solenoids with this K100D, all those work as they should.
The for chosing the K100D is that it can be equipped with AA-batteries and an external PS and I can manipulate the voltage slightly,
in both cases I have more umpfhh... i.e. milli-Amperes. I also have a modified D-BG4 from an old K7 which has inserts for AA's and for Li-Ion so I can really play with voltages. The DC-inputplug of the K100D (similar to K200D) is a simple EIAJ-03 plug, so very easy to use different powersupplies or powersources (all other Pentax with external DC-input use the Hirose MQ172 plug, but the K-S1/S2/70 don't have any DC-Input)


After treatment I couldn't notice any difference in the holding force!
It was (which I expected) identical, no change at all.


The result in AV-Mode: It does not release.

Now, I am not daubting Sergio's success!

I had (stuck) green solenoids which worked again after I just took out the magnet and just put it back in.
But very quickly the old problem returned, stuck again.

I had very clever treated solenoids like this one which came as well from an official repair shop but failed i.e. stuck after a bit more than a year.

But in my case the treatment did not change the holding force nor did it better anything else so it would release.

The uploaded video shows the K100D in AV-Mode, you can see the solenoid trying to actuate but it doesn't.

[sergiogonzalez]

Dear Pentaforum Community.

As promised, I report how my KS 2 continues to work. (lubricated solenoid with graphite in November 2019)
This weekend we made an approximation to the Aconcagua hill, in Mendoza, Argentina, and ascended to 4000 meters. above sea level to enjoy the view of the south wall of this Andean colosso that is almost 7000 meters high above sea level.
Take approximately 80 photos, in a fairly aggressive environment.
Use the automatic mode a lot, as the physical conditions at that height are extreme, to reach the viewpoint of the hill you have to walk 10 hours from the entrance to the park and climb approximately 1500 meters.
I do not miss any photograph, so the tendency of good functioning of the solenoid is so good.
Yesterday I checked and cleaned the camera, after this adventure and found no graphite residue anywhere. Nor in the mirror camera that is connected to the solenoid camera through the mounting of the aperture block.
Attached 4 photos taken, 2 at Plaza Francia, the last base camp of Shouth wall of Aconcagua and 2 at Confluencia the first base camp of The Aconcagua.

I hope this will work!
Greetings to the whole community.

---

Last edited by sergiogonzalez; 05-20-2020 at 06:45 PM.

[sergiogonzalez]

I treated a green solenoid which came from an officially repaired Pentax K30.

This solenoid had failed again and I installed a white Japan solenoid inside this K30, it works very well now.


So I treated this green solenoid with graphited and installed it into a K100D which I have at the moment open for several tests.
The treatment was done as you suggested and I am quite sure that this way no contamination is going to be a problem, one can see that the green PET does change to a darker blackish colour, the PET takes the graphite-dust in. I then cleaned it very well: I used a strong vacuumcleaner, held the solenoid into the hose. Afterwards I cleaned it with compressed air. The plunger was treated first with
the graphite-powder on papter but I felt it would not do much. So I used a graphite pen and rubbed it and afterwards cleaned with the vacuumcleaner hose and then compressed air (which wasn't really necessary). So no daubt, there is no danger of graphite inside the camera!


As you probably know, normally the K100D is equipped with the white made in Japan solenoid.
I have tested filed/sanded and unsanded solenoids with this K100D, all those work as they should.
The for chosing the K100D is that it can be equipped with AA-batteries and an external PS and I can manipulate the voltage slightly,
in both cases I have more umpfhh... i.e. milli-Amperes. I also have a modified D-BG4 from an old K7 which has inserts for AA's and for Li-Ion so I can really play with voltages. The DC-inputplug of the K100D (similar to K200D) is a simple EIAJ-03 plug, so very easy to use different powersupplies or powersources (all other Pentax with external DC-input use the Hirose MQ172 plug, but the K-S1/S2/70 don't have any DC-Input)


After treatment I couldn't notice any difference in the holding force!
It was (which I expected) identical, no change at all.


The result in AV-Mode: It does not release.

Now, I am not daubting Sergio's success!

I had (stuck) green solenoids which worked again after I just took out the magnet and just put it back in.
But very quickly the old problem returned, stuck again.

I had very clever treated solenoids like this one which came as well from an official repair shop but failed i.e. stuck after a bit more than a year.

But in my case the treatment did not change the holding force nor did it better anything else so it would release.

The uploaded video shows the K100D in AV-Mode, you can see the solenoid trying to actuate but it doesn't.

Dear Guest, One thousand apologies for the delay in responding, I have had a lot of work.
I've seen that the test of dealing with graphite in a Chinese green solenoid didn't work for you. The conclusion is simple: there is no graphite left between the mirrors of the holder magnet and the Plunguer. Graphite must remain in this area, to produce a gap between the mirrors that allows the rapid separation of these components when the electrical pulse appears.
Let's do the following reasoning:
a) Solenoid operation is safer when using batteries with better voltage
b) Solenoid operation improves when the reel material has less friction coefficient.
c) Solenoid failures begin after about 4000 shots.
d) Normally the solenoid fails 1 or twice, after the camera has been idle for several hours and after 4000 shots of use.
In this case, there is no other option than the element responsible for this failure is the quality of the material and the design of the Plunguer and the holder magnet.
This material with which the green solenoid is built is aging and its magnetic properties change with the number of hysteresis cycles that it suffers with use.
In certain circumstances, the magnetic remnant, causes the electromagnetic force generated by the coils not to reach to override the magnetic field of the neodymium magnet and the remaining field that is then added.
That's the cause of the failure.
We could solve this by changing the design of the Plunguer to redistribute the currents of Foucault that are surely responsible for the problem and randomly magnetize the Plunguer and the holder magnet. For example, make the Plunguer with a silicon laminated steel (in several layers, such as the core of a transformer), or place a copper coil on the plane of the mirrors (as in a power contactor). But this is expensive and difficult to do.
I raise the following concern.
Although my KS2 works well with graphite and has provided me with thousands of photos without failure and I have had no contamination problems, I decided to disassemble it again and remove the graphite between the mirrors of the Plunguer and the holder magnet.
Leave only pet reels of graphite-treated coils. (As photogem describes changes to a brownish green color)
Then add a piece of tape of Permacel P 222 transparent amber (similar to the one used in the camera to insulate electrical parts) between the mirrors. (If this tape is not available, it can be obtained from some tape material from the same camera)
I proceeded to obtain two tape pieces of 1.5 x 1.5 mm, which is the inner section of the reels of the coils.
These pieces I introduced them into isopropyl alcohol to completely remove the glue that the tape has. Done that, the thick tape is less than 3.7 MIL (0.094 mm).
These pieces of tape, inserted between the mirrors of the Plunguer and the holder magnet, have the same effect as graphite.
They provide a controlled gap that results in a decrease in solenoid retention effort, which does not influence the operation of the shutter block, and causes, if the condition of increased magnetism is given, the electromagnetic field of the coils reach for solenoid is released and makes the operation consistent.
I have performed fast burst tests in automatic mode on my camera, using small file types to be able to take more than 100 photos non-stop, changing the lighting and verifying the operation of the diaphragm. All photos were resolved, which concludes that the solenoid is consistent and allows the shutter block to select the correct aperture in each photo. It is my satisfaction to try to collaborate with the Pentaxforum community and try to improve our camera with its original elements.
With this we have removed the free graphite in the camera that is so worrying.
Attention to greetings.

[sergiogonzalez]

Dear Guest, One thousand apologies for the delay in responding, I have had a lot of work.
I've seen that the test of dealing with graphite in a Chinese green solenoid didn't work for you. The conclusion is simple: there is no graphite left between the mirrors of the holder magnet and the Plunguer. Graphite must remain in this area, to produce a gap between the mirrors that allows the rapid separation of these components when the electrical pulse appears.
Let's do the following reasoning:
a) Solenoid operation is safer when using batteries with better voltage
b) Solenoid operation improves when the reel material has less friction coefficient.
c) Solenoid failures begin after about 4000 shots.
d) Normally the solenoid fails 1 or twice, after the camera has been idle for several hours and after 4000 shots of use.
In this case, there is no other option than the element responsible for this failure is the quality of the material and the design of the Plunguer and the holder magnet.
This material with which the green solenoid is built is aging and its magnetic properties change with the number of hysteresis cycles that it suffers with use.
In certain circumstances, the magnetic remnant, causes the electromagnetic force generated by the coils not to reach to override the magnetic field of the neodymium magnet and the remaining field that is then added.
That's the cause of the failure.
We could solve this by changing the design of the Plunguer to redistribute the currents of Foucault that are surely responsible for the problem and randomly magnetize the Plunguer and the holder magnet. For example, make the Plunguer with a silicon laminated steel (in several layers, such as the core of a transformer), or place a copper coil on the plane of the mirrors (as in a power contactor). But this is expensive and difficult to do.
I raise the following concern.
Although my KS2 works well with graphite and has provided me with thousands of photos without failure and I have had no contamination problems, I decided to disassemble it again and remove the graphite between the mirrors of the Plunguer and the holder magnet.
Leave only pet reels of graphite-treated coils. (As photogem describes changes to a brownish green color)
Then add a piece of tape of Permacel P 222 transparent amber (similar to the one used in the camera to insulate electrical parts) between the mirrors. (If this tape is not available, it can be obtained from some tape material from the same camera)
I proceeded to obtain two tape pieces of 1.5 x 1.5 mm, which is the inner section of the reels of the coils.
These pieces I introduced them into isopropyl alcohol to completely remove the glue that the tape has. Done that, the thick tape is less than 3.7 MIL (0.094 mm).
These pieces of tape, inserted between the mirrors of the Plunguer and the holder magnet, have the same effect as graphite.
They provide a controlled gap that results in a decrease in solenoid retention effort, which does not influence the operation of the shutter block, and causes, if the condition of increased magnetism is given, the electromagnetic field of the coils reach for solenoid is released and makes the operation consistent.
I have performed fast burst tests in automatic mode on my camera, using small file types to be able to take more than 100 photos non-stop, changing the lighting and verifying the operation of the diaphragm. All photos were resolved, which concludes that the solenoid is consistent and allows the shutter block to select the correct aperture in each photo. It is my satisfaction to try to collaborate with the Pentaxforum community and try to improve our camera with its original elements.
With this we have removed the free graphite in the camera that is so worrying.
Attention to greetings.

Dear Pentaforum Community.
I would like to report that the solution proposed on Friday, February 14, 2020, does not work.
It does not work because the tape placed in the gap with the idea of reducing the retaining force of the solenoid, is very thick, in addition to not remaining during the operation of the solenoid in the intended place, because its dimensions in area, are less than the stroke of the Plunguer, and this causes the pieces of tape to be inserted between the coil reels and the magnet holder.
The test that I perform with a quick burst is not valid, as one of the pieces went out of place, and the other did not, which diminished the holding force, and made the test successful. When the second piece of tape came out, dark photo problems began again.
I reassembled the solenoid with graphite in the gap and it began to work consistently again.
Either way I'm going to do a new test that I have in mind to eliminate the use of graphite and keep them up to date.
Best Regards!

[photogem]

Dear Pentaforum Community.
I would like to report that the solution proposed on Friday, February 14, 2020, does not work.
It does not work because the tape placed in the gap with the idea of reducing the retaining force of the solenoid, is very thick, in addition to not remaining during the operation of the solenoid in the intended place, because its dimensions in area, are less than the stroke of the Plunguer, and this causes the pieces of tape to be inserted between the coil reels and the magnet holder.
The test that I perform with a quick burst is not valid, as one of the pieces went out of place, and the other did not, which diminished the holding force, and made the test successful. When the second piece of tape came out, dark photo problems began again.
I reassembled the solenoid with graphite in the gap and it began to work consistently again.
Either way I'm going to do a new test that I have in mind to eliminate the use of graphite and keep them up to date.
Best Regards!

This means there are 2 things to learn:

1. The solution with the tape did not work.

I expected this and also would not agree with it in first place but thought I leave it uncommented for a while as you did invest a lot of effort and though.

The reason why I would not agree with this is for the same reason why the "Russian soldering method" is completly banned now as an option:
The tape, aside of it being hammered and thus prone to be destroyed will lengthen the 2 arms of the plunger/horseshoe same as the soldering "Lada-method"! This puts stress onto the lever the plunger sits on. This was discussed often enough in previous threads, this early Russian Lada-Method was replace by the not so evidently critical but still bad filing/grinding/sanding method.

2. the graphite solution also didn't work! Same as I had no luck when I tried it out.
You still had the graphite "rubbed in" from the last time but after the tape-method failed you got black pictures again!

That's what happened to me when I tried the (really interesting!) graphite method.

Now, you wrote about how difficult it is to find a donor-Pentax for a white solenoid in Japan, but look at it from another side:
Opening and closing the Pentax so many times is not going to made all those threads younger but the opposite, some of them will soon shows the wear and you will need different screws.

The hours of work are well meant but it is what directly translated from the German to English would be called kind of:

worse-bettering or to better it for the worse


(verschlimmbessern is the German verb, schlimm = bad, besser = better)

The solenoid cannot really be improved, it has three parts which would need to be changed:
1. better material and more precise machining for the plunger
2. better material and shaping for the body (PTFE instead of the cheap PET, less airgap)
3. better magnetic properties (holding force)

The measured values do speak for themselves.

I know of a method by means of drilling a tiny hole into the bottomside of each shaft of the plunger and then seal them and thus to lessen at least problem #3, i.e. the too strong holding force.

Others have tried to solve this by edging the bottom side of both shafts:


Both methods worked for a time and then went back to the dark-image-syndrom

[sergiogonzalez]

Dear Community and especially to Photogem:

Thank you for following up on this investigation.

I repeat again that the best solution is the Japanese solenoid with PTFE reels. Unfortunately, I can't get one.

Going back to the list of improvements that should have the Chinese solenoid I decided to stop at the geometry of the same, the constructive tolerance and try to use a better quality material on the surface of the reels, so as to try to improve the item a) of my first Thread.

Checking that the space between the Plunguer and the reels were very large, I decided to place a piece of Permacel p222 tape on one of the rubbing faces, on each of the solenoid reels, as shown in the photograph, which I attached in the Word file below , in order to limit the pitch of the Plunguer in the larger plane of the solenoid and to make the Permacel tape support the larger rubbing that the Plunguer does against the reels of the coils.

I should point out that neither the Plunguer nor the inside of the reels has been dimensionally modified and also that the thickness of the tape is less than 0.01 mm, which makes us limited the space by 0.02 mm. Still, the Plunguer slides freely, but much better guided.

That is if I re-treated the surfaces (Permacel tape included) with graphite before assembly.

This tape is built with Polyimida of very high mechanical resistance (more than 70 lib/" or 12 Kg/10 mm) and heat resistance. Its glue can withstand up to 180°C, in addition to having a high hardness and wear resistance.

See its features in:
https://www.nitto.com/us/en/others/products/group/file/datasheet/NA_P-222_V2_EN.pdf

With this the objective is to achieve a friction coefficient similar to that of PTFE, and to limit as I said the pitch of Plunguer, which is responsible that sometimes one leg can be separated first and the other not, which ends in the blockage of the solenoid and the consequent dark exposure.

As a conclusion the green Chinese solenoid already manufactures very large spaces between the coil reels and the Plunguer and begins to fail when it’s make some wear in the areas of rubbing of the Plunguer, which can be improved with this procedure.

I attach a Word document as explanatory as possible so that they see where and how to place the pieces of tape, and a video of the slow burst operation of the solenoid, where you can see the security with which it’s work.

My Ks2 has already exposed about 100 photos without fail with this modification. I'll keep the community informed as it continues to work. This camera is treated with the utmost care, not exposing any screws to excessive torques, so accessing up to the solenoid will have no consequences.
Hoping to succeed in this investigation, and be able to reuse Chinese solenoids safely.

Best Regards.

[photogem]

Yes, but if the tape gets lose, you have more problems than before.

Better instead of


to reuse the Chinasolenoid

to refuse the Chinasolenoid!

[sergiogonzalez]

Yes, but if the tape gets lose, you have more problems than before.

Better instead of


to reuse the Chinasolenoid

to refuse the Chinasolenoid!

Dear Photogem:

Before refuse! the Chinese solenoid, please read the following post

Best Regards!

[sergiogonzalez]

Dear community.

Having thoroughly investigated the causes that may cause the green (Chinese) solenoid to fail from the diaphragm control of our KS2, K30, K50 etc. cameras, I have come to the conclusion that there are other components within the same control that also influence the failure.
As a first observation we see the following: most cameras begin to fail after 4000 shots and about 4 years after they have been manufactured. This means that both the green solenoid and the diaphragm control block work well in this period, so there would be no need to make any modifications throughout the mechanism.
The design and quality is satisfactory.
We should also note that this is an electromechanical and analog device, which, after a working cycle, will need maintenance.
That said, both green solenoid (Chinese with PET) and white (PTEF) will fail after a more or less short period, because other parts of the diaphragm control block began to introduce interference into electrical signals.
Let's also consider the following specification of our cameras: The maximum number of shots per second that the camera can take is 5.5 frames per second. So the speed limit of the mechanism is at 1/5.5, very slow speed versus 1/6000 that can achieve the shutter curtain.
This maximum firing frequency is precisely limited by the diaphragm selection mechanism which is electromechanical and this time is the longest time our camera takes to materialize each shot. That is, it determines the critical path of the firing process.
Let's follow our reasoning:
When we measure the amount of light with our camera, the microprocessor determines many parameters, including diaphragm aperture.
The sequence of operations to fix the diaphragm aperture would be as follows:
1. The microprocessor determines the aperture of diaphragm
2. When shooting, the motor of the diaphragm control block is activated
3. The diaphragm control block begins to raise the mirror, and move the exhaust wheel of the diaphragm control
4. The sensor mounted on the exhaust wheel, counts the amount of windows carved into the exhaust wheel that correspond to the aperture of the diaphragm determined by the microprocessor.
5. Upon counting these windows, the signal is sent to the solenoid so that the anchors, commanded by the solenoid, is released and fix the diaphragm aperture.
6. The process is completed when the mirror reaches its maximum race, and at that moment the movement of the curtain is triggered at the speed previously determined by the microprocessor.
7. The photo is taken by the sensor completing the application of all selected parameters.

Understood this, it is clear that point 5 is critical, because if the solenoid/anchors assembly is delayed, the exhaust wheel is not fixed and the diaphragm will be closed to the value 22, causing the dark photo.
Electrical signals that interact between the sensor that counts the escape wheel windows, the position of the mirror, and the solenoid signal, pass through a commutator, mounted on a sprocket that commands the movement of the mirror.
If this commutator is not perfectly clean, and properly lubricated to be able to drive the electrical signals that are in the order of a few milliamps, in a fairly fast dynamic situation for the switch, the solenoid and the determination of the correct number of escape wheel windows, will be incorrect and result in the much-feared flaw of dark photos.
Dirt in the commutator contacts, which comes from grease expelling neighboring gears, also tainted by environmental dirt, will cause to increase electrical resistance of the circuit and the movements of the solenoid to be slow or zero .
The fault is isolated.
This commutator is in a place exposed to the atmosphere every time we change a lens. In addition, if the camera is exposed to the sun or high temperature, it is very likely that the grease from neighboring mechanisms will reach the switch. That is why this mechanism will always require maintenance.
I tested to clean the switch using a powerful aerosol degreaser fluid, based on carbon tetrachloride, indicated to clean contacts in applications such as high precision mechanisms and solenoid failure was fixed immediately, starting the camera to operate safely and consistently, with the green solenoid mounted as it comes from the factory.
Logically the switch has started working without any lubrication, which can lead to premature wear, and surely the grease that lubricates neighboring gears has suffered a degradation, so wheels and cams will have to be re-lubricated.
I ask the community for this reason for research to determine what type of conductive lubricant the camera factory uses, originally, to maintain for at least a period of 4 years, the consistent operability of this switch and to enjoy for many years our Pentax cameras.
All these operations have been performed without disassembling the diaphragm control block, and every precaution has been taken so that cleaning fluids do not reach other parts of the camera.
This is a very delicate operation that requires skilled labor.
It remains to be considered that the use of graphite, and subsequently the use of adjustment tapes on the green solenoid, undeniably improved the operation of the camera, as it turned out that the solenoid needed less electrical power to act, and improved its speed of reaction, but this solved the problem while the commutator was able to send that power to the solenoid. When the switch worsened its condition, the failure started again.
The same applies to white Japanese solenoids (PTEF). These for their better quality work with less power, but they will start to fail when the collector can't send it to it anymore.
Also all the other considerations that appeared in the forums coincide with the improvement of the operability of the cameras.
Using batteries that provide more power: compensates for the loss of dirt on the commutator.
Take multiple shots before using the camera when the camera has been unused for a long time: Moves the switch several times improving its conductivity and ensuring its temporary operation.
I attach another PDF document with images of the diaphragm control block supplied in another forum by Photogem (thank Photogem) where you define the names of the parts of the control that are mentioned in this thread.

Waiting for comments

Best Regards.

[photogem]

The same applies to white Japanese solenoids (PTEF). These for their better quality work with less power, but they will start to fail when the collector can't send it to it anymore.

And you know this due to which personal experience/tests?

1. For making such a claim, you would have to have a white Japanese solenoid but you don't, which you made very clear earlier on!

2. The Japan Solenoid does not work with less power!

We have several difference which in combination are very important:

- It's magnet has less strength i.e. holding force.
- The different data of release time and holding force!
- Different material for ALL MATERIALS:
Body (PTFE instead of PET) i.e. much better sliding in and out of the plunger and less wear
Metall: Better alloy


But this is only one aspect!

The most important fact and were you are not only totally wrong but were you make assertions which are untrue,
i.e. what these days could be called "fake news":


3. The white solenoid never has failed, it even never started to fail!

We can refer here comparing the difference of the white Japan-Solenoid and the green China solenoid with a well built car-engine compared to an engine built to inferior standards (China solenoid)

If pistons are lose, you can file and sand around but the result would make any car-engineer laugh!

You can use better lube (oil), clean, polish, add additives... all this is absolutly fine if you don't have access to the (cheap available) real replacement but would be stuck without any chance to obtain it!

But here we are dealing with a small device which is readily and cheap available!

So I find all your efforts in trying to find a sensible repair method if one is really not able to do it otherwise are absoluty fine and noble!

But what I don't find noble is that you make claims which

1. you haven't verified
2. are not true at all but invented