Dark frames or dark expositure problems in KS2, K30, K50, etc.

sergiogonzalez · 12-31-2019, 03:06 PM - **4 Likes**

Hello Pentaforum community:

I am Sergio González Pagliara, from Argentina, electromechanical engineer, postgraduate degree in welding and amateur of photography.
Always admire Asahi Pentax's technology and achieve my first Asahi Pentax ME equipment in 1978. Use it intensively until 2005 without any problems in your electronic exposure system. This equipment featured Asahi Pentax 1:7 lenses and an Vivitar 75-205 telezoom, which still work perfectly today.
I entered digital photography in 2005, with various cameras until finally in October 2015 I decided to have a reflex system again. Having optics in good condition, I decided on a Pentax KS 2 equipped with a DA 18-135 Pentax telezoom, which at the time was a good economic/technical option to re-enter good photography and in passing be able to use the old optics.
Everything went well with the KS 2 until August 2019 and with 7000 shots when the diaphragm opening problems or dark photographs began. At first occasional and then it was aggravated to almost impossible its operation.
So I started researching at Pentaforum and found a Photogem post where it describes the history of the development of solenoids applied in Pentax machines. Here's the link for anyone who wants to read it.
A LITTLE BIT OF HISTORY: Development of the solenoid in Pentax cameras - PentaxForums.com
What struck me most is that the main constructive difference between the green solenoid (Chinese) and the old white solenoid (Japanese) is the construction of the reel. PET green, cheaper material and PTEF white, more expensive Teflon material. This led me to think of some considerations regarding the operation of the solenoid:
a) The PET reel increases the coefficient of rubbing of the Plunguer inside the reel when moving.
b) Batteries after 4 years of use have lost efficiency and their voltage decreases rapidly after being recharged (there are many reviews that using good quality AA batteries on the K50, problem is controlled)
c) The material with which the magnet body is built and the Plunguer himself may have gained some magnetism after many cycles
These three considerations led me to try to control the first. For this I obtained a Teflon-based lubricant (PTEF) which I applied only to the PET reel. The consequence was that the opening Block directly stopped working. When the lubricant is passed to the Contact Mirrors of the Plunguer and magnet body, they are glued by surface tension and viscosity of the lubricant, and the diaphragm was always closed.
In the face of this result, disassemble the solenoid of the camera again, disassemble its parts and whit isopropilic alcohol clean the two reels internally, the magnet body and the Plunguer.
When I reassembled the camera at first its walked well, but after two or three days without using it, its took dark photos again in the first few shots.
This led me to believe that the pulse of electric current sent by the camera does not last more than 1/5 of a second, as the opening block is designed to reach a speed of up to 5 shots per second. If the batteries are already weakened, the rubbing coefient is high, and there is suspicion of remaining magnetisms in the metals, there is no other left for the solenoid to stick and as a result the closed diaphragm. From this reasoning is that some forum participants suggest beveling the edges of the Plunguer and decreasing the area of contact with the magnet body, so that the effects of the three listed causes can be lessened.
Already about to proceed to vary the geometry of the Plunguer, I thought I'd use a solid lubricant. It was a coincidence that on my workbench it had graphite powder for the lubrication of locks. Place a very small amount of fine graphic powder inside each reel, and with a small brush I scrub the Plunguer with this graphite. Mount the solenoid and the camera hasn't failed again. (it is very important to keep the cleaning of the reels and solenoid metals. The fat of the fingers can cause problems)
I have almost 1500 shots after this solid lubrication and the solenoid is doing wonders with a very smooth and safe operation.
The following reasoning may apply:
Graphite decreases the coefficient of pet friction, forms a thin separating layer in the mirrors of the Plunguer and magnet body, which improves or decreases the attraction force that can be generated by the eventual magnetism of the metals. This improvement makes even with weakened batteries the solenoid operates and allows the opening block system to select the diaphragm opening obtained by the processor.
Graphite powder from the soft mine of an HB pencil can be easily obtained.
Logically you should be very thorough in the welding procedures of the cables, observe that the graphite is used in the amount necessary so that it does not contaminate other camera devices, observe the correct alignment of the Plunguer with the rest of the solenoid and the lever of the opening block and ensure that the polarity of the magnet and/or cables is correct.
I'll allow myself to use some Photogem photos to define the names of each part of the solenoid.
My native language is Spanish. I apologize to the community for my little Englishman. I wrote the text in Spanish and translated it into English with an automatic translator. Then correct this translation so that it can be understood.
I hope it will help many to repair their camera at no higher cost and confirm that Pentax is perhaps the best camera on the market.
Best Regards and Happy 2020.

Sergio Gonzalez Pagliara

Attached Files

Parts list of solenoids.docx (459.5 KB, 92 views)

Penview52 · 12-31-2019, 03:58 PM

Good idea of "...remaining magnetisms in the metals " you name that fluid as " aperture blocker grease " or you name it.

swanlefitte · 12-31-2019, 04:02 PM

Love your idea. Great to hear a new approach. Hope I don't need it or anybody. If others try it I hope it succeeds for them also.

**ramseybuckeye** · 12-31-2019, 04:17 PM

Well done, your English is not that bad, you've explained it very well, hopefully it may help some people out!

**microlight** · 12-31-2019, 04:37 PM

Hi Sergio, thanks for this, and welcome!

Vmax911 · 12-31-2019, 06:03 PM

As long as you can contain the graphite powder. In my experience it tends to get everywhere. But sounds like it's working for you.

automorphism · 12-31-2019, 07:49 PM

A fascinating read and analysis of the solenoid. I have a K-50, about 15K shots, and I switched to AA batteries years ago. I don't think I have experienced the aperture block failure myself, but I switched to AA batteries simply because my charger didn't work overseas. After reading about the aperture block failure, I just kept using them in hopes it would stave off the worst. Also most of my lenses use an aperture ring so not the end of the world if it does happen.

It is really cool how you used your engineering skills to analyze this camera and find a solution. Not sure if I'd be brave enough to open the camera but I'll keep this in mind as another possible solution to the problem.

reh321 · 01-01-2020, 07:53 AM

Welcome Sergio,

As an American who owns a K-30, but has never opened it and depends on the words of others, this sounds like an interesting solution. Unfortunately, the member who handled these the most is not available right now for comment, but I do have several of them

1. Like others here, I am concerned about the spread of any powder around my equipment, but as long as that doesn’t become a problem, this seems as good as any solution.

2. I would expect Teflon powder to be a more appropriate lubricant than graphite, but I am not sure how to experiment.

3. Members here have always wondered whether there was also a change in metal allows when production off the solenoids was moved, resulting in a change in magnetic properties, but as long as your solution works ....

4. Members here have speculated that the new plastic might deform more than the old plastic did, but as long as your solution works ...

sergiogonzalez · 01-01-2020, 09:25 AM

Originally posted by Vmax911

As long as you can contain the graphite powder. In my experience it tends to get everywhere. But sounds like it's working for you.

Hello Vimax:
In just the right amount you get trapped inside the solenoid PET reel!
Best Regards

sergiogonzalez · 01-01-2020, 09:39 AM

Dear reh 321: Tank for read my suggestion!
I have experienced this solution on my KS2. I've already had more than 1500 shots and no photo has failed, nor does the camera have graphite contamination on any other component. The solenoid works quickly and smoothly, even in a fast burst, with a much dampened noise that is without graphite. Although the graphite is very invasive, in a minimum amount, it sticks in the PET of the reel and there it is. Also very important is the micrometric thickness layer that forms in the mirrors of the plunger and the body of the magnet, because that layer causes the metal bodies to separate instantly when the current blow occurs in the solenoid coils, and gives the security of operation we are looking for. I will continue to operate my camera to ensure the procedure and keep them up to date
Best regards

sergiogonzalez · 01-10-2020, 05:51 AM - **1 Like**

Good morning Pentaforum community:

Today I write to thank you for welcoming the group, and inform you that my Pentak K S2 continues to work wonders, after subjecting the solenoid to solid lubrication treatment with graphite.
Anyone who is encouraged to perform the operation has no doubt in doing so with the precautions I describe, as it makes it possible to reuse the original solenoid of the camera, which has been electrically, magnetically and mechanically designed to assist the operture block of our Pentax cameras. (the solenoids of other devices, they look the same, but they are different in these three aspects). With this we maintain the originality of our equipment.

Attached are photographs that I take’s with my K S2, of the South of Argentine, taken in Lake Huechulafquen in December 2019, with the lubrication of the solenoid with graphite made in November 2019, and with approx. 1000 shots made without any failures.

I take this opportunity to greet you and wish you very happy 2020.

Sergio Gonzalez Pagliara

Penview52 · 01-10-2020, 06:56 AM

Happy new year too. One of my theory that aperture block occurs due to wrong camera settings like these settings: Ks2 camera with 18-50mm, target is room and dimly lighted, Tav mode, F8, Speed 1/500 , ISO 100-3200 Auto, with flash on, camera fires but no picture just black lcd . Also sets F11, 1/700, same as before settings, no image on lcd. Then i use F5, 1/160, iso 100-1600 auto camera fires and captured image in good result of the same target room. Not tried continuous firing only single shot. Pentax says from their explanation that one reason to blame is the age of camera that aperture block occurs but my camera has only 1200 actual recorded images and YET APERTURE BLOCK OCCURS DUE TO WRONG SET UP. Solenoid is an electrical control that opens the aperture but can not be activated ( not open ) if the settings is wrong to the camera ( this is a software issue ). My canon pretty sure fires what pentax can not, also with sony point and shoot. Pentax needs improvement. Nice photo of your place.

**rogerstg** · 01-10-2020, 08:13 AM

@sergiogonzalez: Wow! Your extensive efforts will likely help many that experience this failure. Kudos.

Originally posted by sergiogonzalez

a) The PET reel increases the coefficient of rubbing of the Plunguer inside the reel when moving.

And/or it may be due to oxidation of the plunger. Early faulty models had extensive visible corrosion, though the newer version may not visibly corrode, but still oxidize enough to increase the co-efficient of friction.

Through your thoughtful work, you've shown that a dry lubricant works, at least initially, and hopefully, long term. I wonder if a sprayable lube that dries, prevents corrosion and is safe for electronics might be useful, perhaps allowing application without fully disassembling the solenoid.

Hornady One Shot is such a product that I use for firearms. It has performed very well in tests for lubrication and corrosion protection. Prior to your work, I'd thought that I would try that first if aperture block affected my KS-2. Your efforts add weight to that thought.

**photogem** · 01-11-2020, 05:11 AM

The first question that arises when thinking of graphite:
Why having a Pentax with WR (i.e. protection against water/moisture AND DUST) and then bring this stuff inside of it?

I use high quality graphite since many years successfully in locks but more against squeaking or rattling noices than as a lube.
If you look closely at graphite, it looks like this:

You don't want this powder inside your Pentax!

The plunger really jolts against the metal inside the PET plastic. It will make the finest powder out of an already very fine powder.
Have you ever taken out carbon-brushes out of an electric motor (drill, washing-machine, vacuum-cleaner etc.)?
Those carbon brushes are made out of graphite. The dust spilled/blown around all over such a motor can be pretty messy.

But it comes worse:

Graphite is diamagnetic!
Inside and around the solenoid with have 2 sorts of magnetism:
1. from the permanent magnet
2. from the electro-magnetig coils (as soon as the solenoid actuates those 2 coils produce a magnetic field which opposes field #1 from the permanent magnet!)

So you have 2 magnetic forces which will push/blow the graphite away from the solenoid, i.e. into your Pentax.

Because graphite, particular when 'hammered" into tiniest dust particles will not stick anywhere it can and will creep into places almost small enough for a virus.

So using graphite inside your Pentax is injecting a virus inside it!

By the way, graphite does NOT grease by itself but by drawing a tiny amount of water to its surface:

https://aip.scitation.org/doi/10.1063/1.1760597
Graphite Properties Page by John A. Jaszczak

Anyway, one finds the good Japan-Solenoid in defunct DSLR Pentax bodies for cheap money.

For understanding more about the differences of the solenoids used by Pentax:
https://www.pentaxforums.com/forums/151-pentax-k-30-k-50/389194-little-bit-h...x-cameras.html

Walkingwolf · 01-11-2020, 06:13 AM - **1 Like**

Thank you photogem for your explanation and warnings. You have done a great deal of research into this issue, all of which has helped many. We naturally want an easy fix and this new graphite idea is intriguing but now I have a better understanding of the potential hazards that graphite may pose.
I only wish that Pentax themselves would provide some information and even some support on this.

01-10-2020, 05:51 AM - 1 Like	#11
sergiogonzalez Forum Member Join Date: Nov 2019 Location: Mendoza Posts: 63 Original Poster	Solucion to rapair solenoid of de Aperture Block of K S2, K 30, K 50 and Others. Good morning Pentaforum community: Today I write to thank you for welcoming the group, and inform you that my Pentak K S2 continues to work wonders, after subjecting the solenoid to solid lubrication treatment with graphite. Anyone who is encouraged to perform the operation has no doubt in doing so with the precautions I describe, as it makes it possible to reuse the original solenoid of the camera, which has been electrically, magnetically and mechanically designed to assist the operture block of our Pentax cameras. (the solenoids of other devices, they look the same, but they are different in these three aspects). With this we maintain the originality of our equipment. Attached are photographs that I take’s with my K S2, of the South of Argentine, taken in Lake Huechulafquen in December 2019, with the lubrication of the solenoid with graphite made in November 2019, and with approx. 1000 shots made without any failures. I take this opportunity to greet you and wish you very happy 2020. Sergio Gonzalez Pagliara Last edited by sergiogonzalez; 05-20-2020 at 06:45 PM.

01-10-2020, 08:13 AM	#13
rogerstg Loyal Site Supporter Join Date: Oct 2007 Location: Rhode Island Photos: Albums Posts: 1,168	@sergiogonzalez: Wow! Your extensive efforts will likely help many that experience this failure. Kudos. Originally posted by sergiogonzalez a) The PET reel increases the coefficient of rubbing of the Plunguer inside the reel when moving. And/or it may be due to oxidation of the plunger. Early faulty models had extensive visible corrosion, though the newer version may not visibly corrode, but still oxidize enough to increase the co-efficient of friction. Through your thoughtful work, you've shown that a dry lubricant works, at least initially, and hopefully, long term. I wonder if a sprayable lube that dries, prevents corrosion and is safe for electronics might be useful, perhaps allowing application without fully disassembling the solenoid. Hornady One Shot is such a product that I use for firearms. It has performed very well in tests for lubrication and corrosion protection. Prior to your work, I'd thought that I would try that first if aperture block affected my KS-2. Your efforts add weight to that thought. Last edited by rogerstg; 01-10-2020 at 03:23 PM.

01-11-2020, 05:11 AM	#14
photogem Site Supporter Join Date: Apr 2015 Posts: 3,517	Why you better avoid graphite and other lube inside you Pentax The first question that arises when thinking of graphite: Why having a Pentax with WR (i.e. protection against water/moisture AND DUST) and then bring this stuff inside of it? I use high quality graphite since many years successfully in locks but more against squeaking or rattling noices than as a lube. If you look closely at graphite, it looks like this: You don't want this powder inside your Pentax! The plunger really jolts against the metal inside the PET plastic. It will make the finest powder out of an already very fine powder. Have you ever taken out carbon-brushes out of an electric motor (drill, washing-machine, vacuum-cleaner etc.)? Those carbon brushes are made out of graphite. The dust spilled/blown around all over such a motor can be pretty messy. But it comes worse: Graphite is diamagnetic! Inside and around the solenoid with have 2 sorts of magnetism: 1. from the permanent magnet 2. from the electro-magnetig coils (as soon as the solenoid actuates those 2 coils produce a magnetic field which opposes field #1 from the permanent magnet!) So you have 2 magnetic forces which will push/blow the graphite away from the solenoid, i.e. into your Pentax. Because graphite, particular when 'hammered" into tiniest dust particles will not stick anywhere it can and will creep into places almost small enough for a virus. So using graphite inside your Pentax is injecting a virus inside it! By the way, graphite does NOT grease by itself but by drawing a tiny amount of water to its surface: https://aip.scitation.org/doi/10.1063/1.1760597 Graphite Properties Page by John A. Jaszczak Anyway, one finds the good Japan-Solenoid in defunct DSLR Pentax bodies for cheap money. For understanding more about the differences of the solenoids used by Pentax: https://www.pentaxforums.com/forums/151-pentax-k-30-k-50/389194-little-bit-h...x-cameras.html

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12-31-2019, 03:58 PM	#2
Penview52 Veteran Member Join Date: Apr 2017 Photos: Albums Posts: 327	Good idea of "...remaining magnetisms in the metals " you name that fluid as " aperture blocker grease " or you name it.

12-31-2019, 04:02 PM	#3
swanlefitte Pentaxian Join Date: May 2015 Location: Minneapolis Photos: Gallery Posts: 4,068	Love your idea. Great to hear a new approach. Hope I don't need it or anybody. If others try it I hope it succeeds for them also.

12-31-2019, 04:17 PM	#4
ramseybuckeye Site Supporter Join Date: Apr 2009 Location: Hampstead, NC Photos: Gallery Posts: 17,288	Well done, your English is not that bad, you've explained it very well, hopefully it may help some people out!

12-31-2019, 04:37 PM	#5
microlight Site Supporter Join Date: Sep 2011 Location: Hampshire, UK Posts: 2,129	Hi Sergio, thanks for this, and welcome!

12-31-2019, 06:03 PM	#6
Vmax911 Pentaxian Join Date: Aug 2007 Location: ABQ Photos: Gallery Posts: 826	As long as you can contain the graphite powder. In my experience it tends to get everywhere. But sounds like it's working for you.

12-31-2019, 07:49 PM	#7
automorphism Veteran Member Join Date: Jun 2015 Location: Ontario, Canada Photos: Albums Posts: 791	A fascinating read and analysis of the solenoid. I have a K-50, about 15K shots, and I switched to AA batteries years ago. I don't think I have experienced the aperture block failure myself, but I switched to AA batteries simply because my charger didn't work overseas. After reading about the aperture block failure, I just kept using them in hopes it would stave off the worst. Also most of my lenses use an aperture ring so not the end of the world if it does happen. It is really cool how you used your engineering skills to analyze this camera and find a solution. Not sure if I'd be brave enough to open the camera but I'll keep this in mind as another possible solution to the problem.

01-01-2020, 07:53 AM	#8
reh321 Pentaxian Join Date: Nov 2014 Location: South Bend, IN, USA Photos: Gallery \| Albums Posts: 23,175	Welcome Sergio, As an American who owns a K-30, but has never opened it and depends on the words of others, this sounds like an interesting solution. Unfortunately, the member who handled these the most is not available right now for comment, but I do have several of them 1. Like others here, I am concerned about the spread of any powder around my equipment, but as long as that doesn’t become a problem, this seems as good as any solution. 2. I would expect Teflon powder to be a more appropriate lubricant than graphite, but I am not sure how to experiment. 3. Members here have always wondered whether there was also a change in metal allows when production off the solenoids was moved, resulting in a change in magnetic properties, but as long as your solution works .... 4. Members here have speculated that the new plastic might deform more than the old plastic did, but as long as your solution works ...

01-01-2020, 09:25 AM	#9
sergiogonzalez Forum Member Join Date: Nov 2019 Location: Mendoza Posts: 63 Original Poster	Originally posted by Vmax911 As long as you can contain the graphite powder. In my experience it tends to get everywhere. But sounds like it's working for you. Hello Vimax: In just the right amount you get trapped inside the solenoid PET reel! Best Regards

01-01-2020, 09:39 AM	#10
sergiogonzalez Forum Member Join Date: Nov 2019 Location: Mendoza Posts: 63 Original Poster	Dear reh 321: Tank for read my suggestion! I have experienced this solution on my KS2. I've already had more than 1500 shots and no photo has failed, nor does the camera have graphite contamination on any other component. The solenoid works quickly and smoothly, even in a fast burst, with a much dampened noise that is without graphite. Although the graphite is very invasive, in a minimum amount, it sticks in the PET of the reel and there it is. Also very important is the micrometric thickness layer that forms in the mirrors of the plunger and the body of the magnet, because that layer causes the metal bodies to separate instantly when the current blow occurs in the solenoid coils, and gives the security of operation we are looking for. I will continue to operate my camera to ensure the procedure and keep them up to date Best regards

01-10-2020, 06:56 AM	#12
Penview52 Veteran Member Join Date: Apr 2017 Photos: Albums Posts: 327	Happy new year too. One of my theory that aperture block occurs due to wrong camera settings like these settings: Ks2 camera with 18-50mm, target is room and dimly lighted, Tav mode, F8, Speed 1/500 , ISO 100-3200 Auto, with flash on, camera fires but no picture just black lcd . Also sets F11, 1/700, same as before settings, no image on lcd. Then i use F5, 1/160, iso 100-1600 auto camera fires and captured image in good result of the same target room. Not tried continuous firing only single shot. Pentax says from their explanation that one reason to blame is the age of camera that aperture block occurs but my camera has only 1200 actual recorded images and YET APERTURE BLOCK OCCURS DUE TO WRONG SET UP. Solenoid is an electrical control that opens the aperture but can not be activated ( not open ) if the settings is wrong to the camera ( this is a software issue ). My canon pretty sure fires what pentax can not, also with sony point and shoot. Pentax needs improvement. Nice photo of your place.

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01-11-2020, 06:13 AM - 1 Like	#15
Walkingwolf Senior Member Join Date: Jan 2016 Location: Calgary, Alberta, Canada Posts: 172	Thank you photogem for your explanation and warnings. You have done a great deal of research into this issue, all of which has helped many. We naturally want an easy fix and this new graphite idea is intriguing but now I have a better understanding of the potential hazards that graphite may pose. I only wish that Pentax themselves would provide some information and even some support on this.