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A little bit of history about the development of the solenoid in Pentax cameras up to the K-70:

The legendary patent named "Automatic Camera Shutter" was applied for July 30, 1968 and granted Jan. 4th, 1972.

You can down load the patent HERE


1. The first very simple solenoid I have found in the Pentax ME and ME-Super.

No permanent magnet yet but only a plunger and an electro-magnet to induce the magnetic force to pull the plunger:



It was in 1983 that Pentax introduced its first SLR which offered fully automatic exposure ("program") mode when coupled with a matching Pentax-A series lens:
The Pentax Super-A (Super Program), followed by the Program Plus (Program-A) in 1984.



This was the first time solenoids where used the way we know it until today up to the Pentax K-70.

2. A very nicely built and sophisticated solenoid:





Not yet a rare-earth-magnet as later used but an alnico-magnet, i.e. an alloy mainly of al-uminium, ni-ckel, co-balt, invented by T.Mishima 1931 in Japan:


Backside:


The solenoid in action:





The force of this alnico magnet pulled a kind of cap connected to the leaver which moved the aperture-mechanism and kept it in place.
Taking a picture, the two coils acting as an electro-magnet receive 3 Volts DC from the cameras battery ( 2 x 1,5V SR44 or 1 x 3-V CR1108).
Those 2 coils cancelled the magnetic force of the permanent magnet and the top-cap opened, the leaver moved. Impedance was 14,3 ohms.


The electro-magnetic coils:


The partnumber given was G-100:


This partnumber G-100 remained the same at least up to the Pentax K20D and K200D, possibly later on as well but I have not yet seen a service manual of those.
Samsung named it G-100 as well in the GX1, GX2, GX10 and GX20.


The next solenoid as we know it was introduced in some the MZ-Series (MZ50, MZ6, MZ7 and a few others up to the 35mm Pentax *ist).
This Solenoid was manufactured by Shinmei Electric Co., Tomioko-Cho, Futaba-gun, Fukushima, Japan (see 3.a) and by TDK, Japan (see 3.b)
Those solenoids were also sold to ALPS and Matsushita.


This first SLR Shinmei and TDK solenoids look identical to the later DSLR made in Japan versions and had the same impedance.
This solenoid was driven with 6V/DC (rated with 4,5V/DC) by the solenoid-driver, impuls-voltage was 6.45V.
Thus the holding-force and body thickness were slightly different and sometimes with opposite polarity. It is not recommended to use it.


3. a) Here a photo showing the 3.rd version of a solenoid, this one I took from a MZ50 tested in a K30:

One can see, the plunger tilts slightly in relation to the round part of the leaver which it moves.

The next drawing shows this early SLR solenoid (i.e. not yet DSLR!):


It has 3.4mm bobbin-size (versus 4mm bobbin-size for the later DSLR-solenoids).

Data Japan-made "SLR" solenoid:
- Operating Voltage DC: 3 - 6V
- Coilresistance: 30 ohms
- Attraction force: 2,2 N min
- Backtension: 0,8 N
- Operating stroke: 2mm


3.b) To make things more complicated, Pentax also used a white Japan made SLR solenoid made by TDK:


The early introduced MA-307-9 was developed for 3-6V use (2 x CR2 /900mA) = so for the 35mm SLR Pentax of the MZ/XZ-Series!

And most important: The bobbin thickness was 4m and not 3,2mm as the Shinmei-version. So even more difficult to differentiate from the DLSR version!

Later they introduced the MA-307-26 für 3,7-6,5V (2 x CRV3/3300mA!) = DSLR *istDS/DL, K10D

What can be seen very cleary is the difference in holding-force (attracting force) and return-force (back-tension)


4. A very different solenoid was used in many other MZ/ZX such as the MZ5 bodies:





4. With the introduction of the Pentax *ist D came the "made in Japan" white DSLR solenoid which never failed in any of those bodies up to the Pentax K-r:


The manufacturer of those solenoids remained Shinmei, Japan and manufacture was in Japan.


The next drawing shows that this new introduced Shinmei Japan solenoid for DSLR bodies had now a 4mm bobbin-size instead of 3.4mm:


As mentioned, this difference of 0.6mm is hardly noticable but this is why aside from another small difference in holding-force and often opposite polarisation the early SLR solenoids with 3.4mm bobbin-size sit slightly bent when installed into a DSLR body!
This DSLR Solenoid had a live-timespan of remarkable 100.000 actuations but lasts actually much longer.


Data Japan-made "DSLR" Solenoid:
- Operating Voltage DC: 3,6 - 7,2 V- Coilresistance: 30 ohms
- Attraction force: 2,5 N min
- Backtension: 1,0 N
- Operating stroke: 2mm

According to an engineer who worked for Pentax and with teams designing cameras (I have the email from him as prove)as well according to a Ricoh representative from France the material used was a mix of PTFE's (Teflon) and thus it could be injection molded. I cannot guarantee this to be the case but there is no reason not to believe specialists.



5. Green-China-Solenoid

When Shinmei moved production to China, difficulties started!
Shinmei was now the sole provider to Ricoh for Pentax DSLR cameras!

Manufacturing place was now in Shanghai. Problems due to saving costs arised, such as bad pay and bad treatment of workers

Manufacture in Tomioka, Japan, stopped earlier on but the plant itself was finally shut-down in 2010.
This means not more manufacturing possible in Japan.


The material of the body changed to the green colour and instead of using a mix of different PTFE's (teflon) it was now made out of PET.

The alloy of the plunger changed as well.

PTFE (teflon) is a very good bearing material, it is used as well for bearings in turntables. This bearing was patented by W. Firebough. He describes the bearing very well in This interview. I could verify the amazing bearing qualities myself. When one inspects a heavy used Japan-solenoid closer against one made in China, one can tell the difference, PET is worn off much quicker.

This China made solenoid was first used in the flash circuit of the Pentax K100D (year 2006), K100D, K200D, K-m, K-x and K-r (until year 2011) but as far as I know mainly in those delivered to Europe. So a testing period of 5 years without any failure.

Rated voltage was now 3,7 - 7.5V (impuls 8.32V) but live-time was drastically lower: 20.000 actuations.

Data China-made solenoid
- Operating Voltage DC: 3,7 - 7,5V
- Coilresistance: 30 ohms
- Attraction force: 2,8 - 3,0 N min
- Backtension: 1,2 N
- Operating stroke: 2mm


Here you can see the measurements on a Pentax K-30


The next drawing shows the datasheet of the green China-solenoid:

The dashed (----) line shows the 30ohms version used for Pentax. The lower live-time of 20.000 actuations is due to PET instead of PTFE used in the early Japansolenoid.

Some claim (without prove, because it cannot be proven) that the voltage used for the Chinasolenoid would be more in the region of 2.5V because it releases smoothly at 2.5V. That's a lot of nonsense because none, the early Japan made SLR, the next Japan made DSLR solenoid nor the China made version work well with just 2,5V/DC! They kind of work with 3V but are driven with 6V in the SLR Pentax cameras and 7.2V in the DSLR Pentax cameras.
If one studies the curve for holding-force one can see this very clearly! I have done tests with 3V, 6V and 7.2 Volts. Measuring release-time (and thus holding-force) can be done from 5V - 9V. If one compares different solenoids it just is important that the applied voltage is the same for all solenoids one compares! The applied Vpp since the Pentax *ist-D is exactly 8.32VDC. Earlier pre DSLR bodies such as the MZ50 had 6VppDC.

The solenoid is driven by a transistor (BJT/SOT23) and protected by a simple diode.


While the China-made solenoid was tested in the flash-circuit, the solenoid used for aperture-control remained still the white made in Japan unit!
This test-period went on for about 6 years (the K100D was introduced 2006, the K-30 introduced 6 years later in 2012).
So 6 years without trouble, enough time to use it for the aperture control.

This photo shows the green China solenoid for the pop-up-flash in a K200D:



And here built out:




This change to manufacture in China turned out to be the beginning of difficulties due to several reasons described here as well
and led to a problem now known as:

ABF = Aperture Block Failure (also named: "dark-image-syndrome" or "dark exposure problems")

The plunger of this solenoid suddenly didn't release anymore but remained stuck! The diaphragm/blades/aperture of the lens could not open and
thus particular wide open and low f-stops (f1.4 / 1.7 / up to f 8) resulted in totally underexposed pictures, almost dark/black. If one changed to fully closed (such as f22) one gets a normal exposed picture.

For quite a long time it was not yet clear that the cultprit was just the solenoid!

The complete "diaphragm-control-block" was exchanged or possibly just the whole camera because exchange of the block was very work + time intensive. But then due to all the research mainly here in this forum (!) Ricoh/Pentax realized that it was just the solenoid itself.

It was about Dec. 2015 that Ricoh started to modify the solenoid which we now call the

6. "2.nd generation China-Solenoid":

But quite a lot KS-1's, K-S2's and many K-50's and all K-500's still used the earlier 1.st generation China-made green solenoid because they were manufactured prior Dec.2015! Thus quite a lot of them failed and do still fail.

This is mainly due to fact that the metal body + plunger of the China-Solenoid is made out of relatively higher coercivity material:
It thus retains its magnetism after the field strength is removed!

This also explains why in many cases ABF happens more to those Pentax bodies which hadn't been used for a longer period and/or those with a low shuttercount (a low shuttercount implies little use anyway up to the case of two NOS Pentax bodies which I repaired, they hadn't been used at all but cought ABF, so the best proof for this explanation which I got from a forum-member who is a Chartered Electrical Engineer with Nuclear Electric.

It is very simple: When the Pentax is not used the plunger sits all the time near the permanent magnet and the magnetized body.
No use will enhance the "glueing effect", i.e. the solenoid sticking inside the body.
Regular use is no guarantee but it is clear and researched that ABF happens less often.

!!! The holding force of this 2.nd generation China-Solenoid was still stronger compared to the Japan-made Solenoid !!!
and it does not fire as quick.


Close-up photos of the solenoid used in the K-70 show now a very nicely machined plunger with a smoother surface:



Very different to the surface of a solenoid modified by filing or sanding:

The surface of the alloy which is hurt by sanding or filing starts to corrode and can actually rust pretty bad.


So due to the still stronger holding-force and the alloy
it turned out that this 2.nd generation China-made solenoid wasn't perfect yet!

ABF happened less but there were still reports of K-70's failing.

Some repairshops tried to deflect from the true cause (the solenoid) and invented a socalled "resistor-chip" which now would fail and cause the solenoid to stop working correctly. We had some hot heated discussions about it, it turned out to be a fairytale and the repairshops quickly stopped "exchanging resistorchips".


6. Fake Solenoids (but recommended by their sellers to be suitable for Pentax = Fake facts)

a) Meanwhile more and more green solenoids turned up on ebay, ali-express etc.
If purchased in quantities via alibaba China one single solenoid was just a few cents, BUT:
Those are even inferior and were NOT MADE FOR DSLR but for Lenovo DVD-drives:


You can see, the 2 pins facing sideways are missing!

The permanent magnet is longer and stronger and thus they have a way too strong holding force!

They were constructed for a very simple "press-button-open-tray" circuit


Beware of those by all means!


b) Beware of Blue-coloured China-Solenoids from ROM-Drives:

Wrong impedance (15ohms)! Danger of exodus for the "solenoid-driver".


c) And of course:Beware of green solenoids which are filed/sanded!

Further information why you should avoid this you can study HERE

d) Some sellers on ebay offer white Japan solenoids which actually are SLR solenoids, no matter if 4mm bobbin-size made by TDK!
See 3.b)

Further Warnings: (based on long-time and verified studies)

- Lubing: Beware of any attempt to lube the plunger of the solenoid!
Even very thougthful attemps or rubbing graphite-powder into the plunger didn't solve it.
WORST Scenario I ever came across was to spray contact-cleaner or similar stuff from HERE, i.e. the mirror-box towards the region of the solenoid. You don't want to spray anything inside your camera, most sprays contain oily ingredients such as naphta or petroleum together with fast evaporating ingredients to make it dry quickly. The worst that can happen is if such stuff comes into contact with the mirror or hinged submirror, damping material for the mirror, the shuttercurtain of your sensor.
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With the Pentax K7 Pentax introduced a stepper-motor instead of a solenoid. This demands a different powersupply, more current from the battery, extra space within the body, i.e. the body has to be larger plus some weight. This stepper-motor was used in the K7, K5, K3, KP and K1.

Size comparison of the stepper motor on its board against the solenoid:

7. GOOD NEWS:
3.rd generation green China-solenoid used since Jan. 2021 in the K-70
and of course now the KF:


Shinmei changed the size of the magnet, it is again shorter and thus has less magnetic power.

Here you can see all 3 stages of the China-solenoid (plus the very bad Lenovo solenoid on the right side):



So we have 3 steps of the China-made green solenoid used since the K-30 in the aperture block:


- Verson 1: The non-modified version as we know it was used until Dec. 2012, less clear defined dimple in the plunger

- Version 2: The 1.st modification as used since Dec. 2012 with a smaller magnet, changed alloy and clear defined dimple in the plunger

- Version 3: The 2.nd modification: Same alloy as in the 1.st modification but even shorter magnet (since Jan. 2021)

[lesmore49]

I'm probably missing something, but I have a Pentax ES ll that I bought new in '74 and it has an automatic shutter, program, etc...and there was a forerunner of the ES lll, the ES which came out in the very early '70's with an automatic shutter. The were both screw mounts.

I don't know enough about electronics to know if they had solenoids. Maybe not.

I'm no expert, so perhaps I've misunderstood, but I still have my ES ll and it still works on 'automatic,

[photogem]

I'm probably missing something, but I have a Pentax ES ll that I bought new in '74 and it has an automatic shutter, program, etc...and there was a forerunner of the ES lll, the ES which came out in the very early '70's with an automatic shutter. The were both screw mounts.

I don't know enough about electronics to know if they had solenoids. Maybe not.

I'm no expert, so perhaps I've misunderstood, but I still have my ES ll and it still works on 'automatic,

AUTO on a Takumar lens has nothing to do with the A-setting of lenses that were introduced with the SMC-A lenses and automatic or semi-automatic (Av, Tv, Tav etc.) modes which is "triggered" by the solenoid.

The AUTO-setting on a Takumar and the later Super-Takumars is well explained HERE

So no, the ESII has no solenoid.

Recently somebody mixed up the AUTO-Setting on the Mode-dial with the AUTO/M-Switch on the Takumars.

[reh321]

I'm probably missing something, but I have a Pentax ES ll that I bought new in '74 and it has an automatic shutter, program, etc...and there was a forerunner of the ES lll, the ES which came out in the very early '70's with an automatic shutter. The were both screw mounts.

I don't know enough about electronics to know if they had solenoids. Maybe not.

I'm no expert, so perhaps I've misunderstood, but I still have my ES ll and it still works on 'automatic,

Your “ES II” is excluded from ‘abf’ effects in any case - just as my “Super Program” of ten years later is excluded - because they used Japanese-made solenoids, and ‘abt’ occurs only with the change of materials and possible workmanship changes that occurred when production later moved to China.

[photogem]

Your “ES II” is excluded from ‘abf’ effects in any case - just as my “Super Program” of ten years later is excluded - because they used Japanese-made solenoids, and ‘abt’ occurs only with the change of materials and possible workmanship changes that occurred when production later moved to China.

This is wrong and you know that, so I ask myself, what is the reason for your post?!

As I have clearly showed in the main article, the "Super-Program" (Super-A) and then the "Program Plus (Program-A) were the first Pentax using a solenoid
relativly similar in construction to the later SLR and particular DSLR solenoids:

But it is still very different to the Japan-made "DLSR-solenoid" with a moving plunger and not a moving magnetic-cap:

That type of solenoid with a moving plunger and the magnet in the top holding the plunger in position was first intruduced in 1997 with the MZ50.



THE ESII DOES NOT USE ANY SOLENOID!

I made that very clear in my previous message!

So I don't understand:

Why Do you write something that you know isn't true?
You have done so in the past:
Solenoid in Pentax K-70 - Page 4 - PentaxForums.com
Here I made it very clear to you but you still seem to have this urge to write something that by now you know isn't true:
New K-70 and Aperture Block - Page 5 - PentaxForums.com
Why?

May I remind you of that very sensible advice:

Enough already reh321: This thread is already 49 pages long.
Ask yourself before posting:
Are you adding new information, data, insights to the discussion?

Of course you don't add any new information, not even old information but wrong information!
As you had been corrected about this error several times: Is there any intention behind that?
How can it be brought over to you finally?


Also:
Why do you invent some new word called "abt" when since a long time we speak about Aperture-Block-Failure = ABF?

The main article is clear enough, every information is right there.

---

Last edited by photogem; 10-20-2021 at 05:49 AM.

[reh321]

This is wrong and you know that, so I ask myself, what is the reason for your post?!

As I have clearly showed in the main article, the "Super-Program" (Super-A) and then the "Program Plus (Program-A) were the first Pentax using a solenoid
relativly similar in construction to the later SLR and particular DSLR solenoids:

But it is still very different to the Japan-made "DLSR-solenoid" with a moving plunger and not a moving magnetic-cap:

That type of solenoid with a moving plunger and the magnet in the top holding the plunger in position was first intruduced in 1997 with the MZ50.



THE ESII DOES NOT USE ANY SOLENOID!

I made that very clear in my previous message!

So I don't understand:

Why Do you write something that you know isn't true?
You have done so in the past:
Solenoid in Pentax K-70 - Page 4 - PentaxForums.com
Here I made it very clear to you but you still seem to have this urge to write something that by now you know isn't true:
New K-70 and Aperture Block - Page 5 - PentaxForums.com
Why?

May I remind you of that very sensible advice:

Of course you don't add any new information, not even old information but wrong information!
As you had been corrected about this error several times: Is there any intention behind that?
How can it be brought over to you finally?


Also:
Why do you invent some new word called "abt" when since a long time we speak about Aperture-Block-Failure = ABF?

The main article is clear enough, every information is right there.

I usually post on my smart phone and make occasional spelling errors;
this part of your response was such a trivial response - not a big deal at all.

My response was an attempt to correct some misunderstanding shown in the comment I responded to.
I thought I was in basic agreement with you.
I’m sorry you apparently did not approve and apparently felt a need to correct me.

My post stated there is a difference between what was produced in Japan and what is now produced in China - that was my purpose.
Do you disagree with my main point?

[photogem]

I usually post on my smart phone and make occasional spelling errors;

Understood....

.. this part of your response was such a trivial response - not a big deal at all.

In retrospect yes, agreed.

My response was an attempt to correct some misunderstanding shown in the comment I responded to.

Somehow I felt it led to further confusion. Maybe still a problem of language.

Member @lesmore49 asked if the ESII has solenoids, I answered "no".

So when you responded with:

Your “ES II” is excluded from ‘abf’ effects in any case - just as my “Super Program” of ten years later is excluded - because they used Japanese-made solenoids.....

I read that as "not agreeing" with what I wrote, i.e. I still understand your message saying "they (i.e. ES II + Super Program) used Japanese made solenoids.

I guess you just didn't write this message clear enough?!

[reh321]

Understood....

In retrospect yes, agreed.

Somehow I felt it led to further confusion. Maybe still a problem of language.

Member @lesmore49 asked if the ESII has solenoids, I answered "no".

So when you responded with:

I read that as "not agreeing" with what I wrote, i.e. I still understand your message saying "they (i.e. ES II + Super Program) used Japanese made solenoids.

I guess you just didn't write this message clear enough?!

We have had our disagreements in the past. I understand how someone from Switzerland might not understand the political implications to an American of identifying a solenoid as “from China”.

I previously said there was no acceptance test to weed out the solenoids that would fail. Perhaps outside lawyers - possibly aided by {expensive} outside engineers, have found a test that works, but we still don’t know if it matters enough to Pentax for this knowledge to change their ways.

[MarkJerling]

Thats for the additional photos @photogem.
So, even smaller magnet in the latest versions. Very interesting.

[reh321]

I purchased my “Super Program” in 1983 and then used it for over 12 years - the longest I’ve used any camera - and periodically since then. When I last used it {a year or two ago} the aperture control mechanism still worked, so there was nothing wrong with the concept - just the recent implementation {I.e., the part used}.

[hatsofe]

Very interesting! Thank you for posting this history of the development of the solenoid.

Thank you! Great article, very detailed with meticulous approach to subtle nuances. . We managed to fix this problem in K70 after getting a white solenoid from eBay. The only thing : should I lock the screw that holds the solenoid in place with a glue?Initially it was locked with some kind of resin, apparently to prevent self loosening as a result of vibrations.

---------- Post added 06-03-22 at 07:22 PM ----------

Update:
*istD has 2 solenoids, one in the flash-circuit, one for aperture/diaphragm-control
*istDS and DS2 (as well as Samsung GX1s) have only 1 solenoid (Aperture)
*istDL/2 (Samsung GX1L) have again 2 solenoids


1 solenoid to be found in K10D, K20D (Samsung GX10/20) as well (Aperture)

2 solenoids to be found in:
K100D, K110D, K200D, Km(K2000), Kx, Kr (but in EU and Switzerland most of those have already the green solenoid in the flash-circuit!)


1 green solenoid to be found in:
K30/50/500/KS1/KS2/K-70

modified better green solenoid found in:
K50/K-S1/K-S2 from December 2015 onwards
K-70

Thank you! Great article, very detailed with meticulous approach to subtle nuances. . We managed to fix this problem in K70 after getting a white solenoid from eBay. The only thing : should I lock the screw that holds the solenoid in place with a glue?Initially it was locked with some kind of resin, apparently to prevent self loosening as a result of vibrations.

[photogem]

Thank you! Great article, very detailed with meticulous approach to subtle nuances . We managed to fix this problem in K70 after getting a white solenoid from eBay. The only thing: Should I lock the screw that holds the solenoid in place with a glue?
Initially it was locked with some kind of resin, apparently to prevent self loosening as a result of vibrations.

Hello and well done, I saw you used the K-70 tutorial.

Pentax used some red thread-locking-laquer Pentax. As I came across some older versions were no such laquer was applied I never felt the need to use it, the solenoid nor the fixing screw ever came loose.
But if you want to play save, you could use some nailvarnish instead, if no thread-locking laquer at hand.

In the K30/50 tutorial as well in the K-S1-tutorial I mentioned this laquer but later on no longer as I stopped using it.

[brofkand]

The K-70 we use at work needs a new solenoid. Where do I go to get one? I see them on eBay with prices ranging from $10 (shipped from Belarus) to $45 shipped from Japan. What is the recommendation?

[photogem]

The K-70 we use at work needs a new solenoid. Where do I go to get one? I see them on eBay with prices ranging from $10 (shipped from Belarus) to $45 shipped from Japan. What is the recommendation?

Only this one on ebay:
Pentax K-30 K-50 K-70 K-S1/S2 K-500 Genuine White Solenoid Part - Japan - | eBay (this is the only "made in Japan DSLR" version*)

The Belarus version (as well as the one fron Poland!) isn't even one for Pentax but for DVD-ROM drives and can be recognized by the blue color.
Those usually have 15 ohms only (and the largest magnet, i.e. way way stronger holding force).
There are no Japanese sellers.

There are 2 sellers from Europe.
a) one from Germany (kilo404): Not DSLR but SLR version (he at least indirectly mentions it)
b) one from UK (randr2012): Not DSLR but SLR version

clever disguised as he writes:
"This is an original solenoid plunger removed from a donor camera, these solenoids were made in Japan and lastly used in K-r and K-x."

*I have zero connection to the seller potmano in USA!

[hatsofe]

The K-70 we use at work needs a new solenoid. Where do I go to get one? I see them on eBay with prices ranging from $10 (shipped from Belarus) to $45 shipped from Japan. What is the recommendation?

We used the solenoid that photogem mentioned in his answer to you ( Pentax K-30 K-50 K-70 K-S1/S2 K-500 Genuine White Solenoid Part - Japan - | eBay ). We replaced the solenoid two days ago and checked it out in action yesterday. The camera functioned flawlessly. So far so good.
Advice: mark down each screw position while removing the outer casing, because there are three-four groups of different length screws in it. The depth of each screw hole, of course can be verified with a simple needle , but marking them (positioning on a sketch against their proper holes, for example) during disassembling avoids confusion and time waste later. Also: there is a small round washer- like spacer that seats(I hope, that is where it was !) around a microphone connector ,which falls off when you remove the side panel.

[photogem]

Remember:
This is not the tutorial thread but it is the thread for the history of the solenoid!
Further posts please either in the "DIY section":
Do-It-Yourself - PentaxForums.com

or here in the DSLR specific section:
DSLR-Specific Forums - PentaxForums.com
Thanks!