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A LITTLE BIT OF HISTORY: Development of the solenoid in Pentax cameras
Posted By: photogem, 06-27-2019, 01:50 AM

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.
-----------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------


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)








Last edited by photogem; 09-28-2023 at 06:17 AM. Reason: Latest info added by Photogem
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08-11-2022, 12:41 AM   #121
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Jopie890 wrote: If i look at user Morton china green solenoid i have to conclude his one is also a non-modified original one, would be handy yo know his manufacturing date of his K-S2.
My K70 was bought new in early 2018, serial number is 7341646. I have no idea when it was made. But it has had irregular use for a total of 4,312 shutter operations over 4.5 years.

08-11-2022, 12:50 AM   #122
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QuoteOriginally posted by Morton Quote
Jopie890 wrote: If i look at user Morton china green solenoid i have to conclude his one is also a non-modified original one, would be handy yo know his manufacturing date of his K-S2.

My K70 was bought new in early 2018, serial number is 7341646. I have no idea when it was made. But it has had irregular use for a total of 4,312 shutter operations over 4.5 years.
You can find the manufacturing date here.
https://www.pentaxforums.com/pages/check-shutter-count-exif.html
Alternatively you can use Exiftool to find it in the Maker Notes of the Exif data.

08-11-2022, 01:06 AM   #123
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QuoteOriginally posted by slartibartfast01 Quote
Third mod? How many mods have there been? I thought there was one in December 2015 and the recent one.
That's right, there was the

1.st modification December 2015
2.nd modification with the K70 possibly around 2020 but nobody knows for sure.

It was December 2018 when the main representative from Ricoh Paris/France wrote to me, that "a new solenoid was used in the K-70".
We were in contact because a few K70's developed ABF and members of the German/Suisse forum got worried.
This was then the 12/2015 (1.st.generation) modification.

Another tiny difference was, that in the K70 the screw fixing the solenoid to the controlunit itself is located on the left side (no real difference of course).

@Stevebrot started a report in 10/2018 until 12/2019:
K-70 Underexposed Photo Reports - PentaxForums.com
If you read #149, this was dedicated towards me myself.


Further attemps to distract away from the solenoid being the culprit sometimes went very curious/funny ways:

Some repairshops invented a so-called resistor-chip which would fail. Too much voltage would pass now through the solenoid which in turn would go bad.

This was really the funniest invention because there exists no resistor-chip in any Pentax-circuit driving the solenoid, there are resistors, yes, and there is a diode which protects (but none of those ever went damaged!). Of course one could call a diode a resistor because "it resists" into one direction and allows the voltage into the other.

Today I have a K70 on my workbench, manufactured 6/2017.
The solenoid in there: 2-nd generation, i.e. 1.st modification (clearly to be seen on the attached photo)
Low shuttercount, typical failure.

It was December 2018 when the main representative Tohru Kodama from Ricoh Paris/France wrote to me:
"The solenoid in the K-70 is new and differs from the ones used in the older K-30 and K-50 models."

We were in contact because a few K70's developed ABF and members of the German/Suisse Forum got worried.
This was then the 12/2015 modification. But in the K70 the screw sat on the left side now (no real difference of course).
Attached Images
   

Last edited by photogem; 12-09-2022 at 12:08 AM.
08-11-2022, 01:12 AM   #124
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QuoteOriginally posted by photogem Quote
Useful to know:

How many solenoids has one changed, how many Pentax DLSR for that reason disassembled?
And how many checked for manufacturing date?

Nevertheless:
It is possible that at the assembly-place workes took an early production solenoid.
If one takes into account how very badly workers there are paid, one shouln'd be surprised if not everything goes "by plan"

What really counts
1. "Holding force" and this can either be measured or "sensed" if you know how-to. If you don't have sensitivity in your fingers,
you are more or less similar unsensititive to good food because your sensitivity is measure by McDonalds or similar deep frozen hamburgers, hot-dots and/or similar junk-food,
so no much value... and I won't bring in good wine or .... a good eye

2. The quality of the alloy, almost impossible for us to "measure"

All this is quite unimportant:
We know that the white DSLR Japan Solenoid never failed... I have measured its qualities and that is all we need to know!
Isn't it odd that my solenoid from a K-50 manufactured in August 2014 before any modifications seems to have a shorter magnet than one from a camera manufactured in 2017?



08-11-2022, 01:24 AM   #125
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QuoteOriginally posted by Morton Quote
Jopie890 wrote: If i look at user Morton china green solenoid i have to conclude his one is also a non-modified original one, would be handy yo know his manufacturing date of his K-S2.
My K70 was bought new in early 2018, serial number is 7341646. I have no idea when it was made. But it has had irregular use for a total of 4,312 shutter operations over 4.5 years.
Here you can check when it was manufactured:
Check Camera Shutter Count and Manufacture Date
The K70 I repaired today has a serial of 733377xx and it was manufactured 6/2017.
So I am curious when yours was made! Shuttercount on yours is pretty low.
08-11-2022, 01:31 AM   #126
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QuoteOriginally posted by slartibartfast01 Quote
Isn't it odd that my solenoid from a K-50 manufactured in August 2014 before any modifications seems to have a shorter magnet than one from a camera manufactured in 2017?
Odd yes, but I observed something that could explain it:
A German dealer sold really large quantities of K50's and later K-S1's as new but ex-demonstration units allegedly from Pentax-shows!
I got a few of those onto my work-bench. It had turned out that they were repaired, i.e. solenoid replaced!

I don't think any were from shows but just got their solenoids replaced either for security or because they already had developed ABF.


Even a brandnew never used Pentax with the wrong solenoid can develop ABF!
I had a few with very low shuttercount, the lowest as far as I can remember was 6.

But you know what is more odd:

The magnet of your China-Solenoid seem inbetween 1st and 2nd modification.
If you look closely at the picture I have in my main post, the magnet of the 3-rd generation solenoid is shorter, their is an (air-) gap at the top as well! If you'd move this magnet upwards, its lower end would be almost at the center of the two holes!
08-11-2022, 03:21 AM   #127
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My screw on the non modified green solenoid of my 2017 K-S2 was also on the left side, the camera has around 4000 clicks and was bought new in Amsterdam at Kamera-express in january 2018

08-11-2022, 06:03 AM   #128
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QuoteOriginally posted by photogem Quote
Here you can check when it was manufactured:
Check Camera Shutter Count and Manufacture Date
The K70 I repaired today has a serial of 733377xx and it was manufactured 6/2017.
So I am curious when yours was made! Shuttercount on yours is pretty low.
As you know, shutter count seems to have zero effect on developing ABF.
The real issue seems to be calendar age of use.
Once a lower tier camera body is around two years old, it seems to be a candidate for ABF,
because it seems to had time to magnetize the solenoid.
I purchased my K-30 with a shutter count of 3. I used to think that it had developed ABF ‘early’ despite my using AA batteries,
but perhaps it developed ABF late since the process of magnification may have started before I ever got it, and my use of AA batteries may have delayed the inevitable.

Last edited by reh321; 08-11-2022 at 06:50 AM.
08-11-2022, 10:23 AM - 1 Like   #129
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QuoteOriginally posted by Joepie890 Quote
My screw on the non modified green solenoid of my 2017 K-S2 was also on the left side, the camera has around 4000 clicks and was bought new in Amsterdam at Kamera-express in january 2018
The side of the screw is not really important because it just defines a difference of the socalled "diaphragm-control-unit"!
That is the block which was introduced as pictured with the K-30.

As soon as ABF became known, many Pentax repairshops replaced the complete unit which of course was pretty useless because it was only the solenoid which failed.

So I won't go into deep explanation but just to make sure: The side of the screw is totally unimportant!
More information is not needed.
08-11-2022, 08:04 PM   #130
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QuoteOriginally posted by photogem Quote
Here you can check when it was manufactured:
Check Camera Shutter Count and Manufacture Date
The K70 I repaired today has a serial of 733377xx and it was manufactured 6/2017.
So I am curious when yours was made! Shuttercount on yours is pretty low.
Thanks Photogem. Your link to the Forum's shutter counter & DoM shows my K70 was made on 2017:10:04. So, 4th of October, or 10th of April, in 2017. I bought it on 17th January 2018, so it was very new.
12-09-2022, 12:10 AM - 2 Likes   #131
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QuoteOriginally posted by Morton Quote
Thanks Photogem. Your link to the Forum's shutter counter & DoM shows my K70 was made on 2017:10:04. So, 4th of October, or 10th of April, in 2017. I bought it on 17th January 2018, so it was very new.
Then it has the 2.nd generation made in China solenoid inside.
The 3.rd generation solenoid (which is fine and will be also in the KF) was introduded in 2021. When exactly I don't know but pretty early because I never had a K70 manufactured in 2021 or 2022 on my workbench. Only older versions.
12-09-2022, 11:07 PM - 2 Likes   #132
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QuoteOriginally posted by photogem Quote
Then it has the 2.nd generation made in China solenoid inside.
The 3.rd generation solenoid (which is fine and will be also in the KF) was introduded in 2021. When exactly I don't know but pretty early because I never had a K70 manufactured in 2021 or 2022 on my workbench. Only older versions.
Thanks Photogem. This has been a very interesting and useful thread.
01-17-2023, 08:42 AM   #133
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QuoteOriginally posted by photogem Quote
The 3.rd generation solenoid (which is fine and will be also in the KF) was introduded in 2021.
Is there a way to source a 3rd generation solenoid? My KS2 is starting to show some signs of aperture block failure. I don't use my KS2 with any regularity, so it's not much of an issue, but I'd like to fix it.
01-17-2023, 10:12 PM   #134
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QuoteOriginally posted by Kozlok Quote
Is there a way to source a 3rd generation solenoid? My KS2 is starting to show some signs of aperture block failure. I don't use my KS2 with any regularity, so it's not much of an issue, but I'd like to fix it.
Not in the USA and shipping from UK (the only seller there, John Pye, doesn't ship abroad) or EU would make it more expensive than buying the Japan DSLR Solenoid on ebay.com (seller potmano)

I still prefer the Japansolenoid, it has served well since the *ist-D and never failed.
The K-S2 is worth it
12-08-2023, 12:09 PM   #135
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A few weeks ago a person in a German forum complained that his K-30 which had ABF and which he repaired with a China-Solenoid purchased on ebay still didn't work after the solenoid was replaced. He pointed at another K-30 which seemed to have the same problem and which was on offer with ABF-defect on a platform called "Kleinanzeigen".

I contacted this seller, he told me that long time ago he had purchased a cheap ebay China-Solenoid, replaced it but the ABF didn't go away.
He then gave up and now offered it for a very cheap price on Kleinanzeigen.
So I purchased his K-30 (all email conversation is with me as proof) and the results were obvious:


Photo 1: Shows the China Solenoid in this K-30!

It is the China-Solenoid how it was sold on ebay a few years ago, still with side pins but the very large magnet!

This magnet is larger and (and thus stronger) than any China-solenoid ever used by Pentax
(i.e. what is called 1.st generation solenoid in the main post of this thread!)

The magnet and its holding force is 100% identical to the so called "fake Lenovo-solenoids" now on offer on ebay and Aliexpress!
The only difference are the missing side-pins which makes it even more vulnerable, because the PET melts very easely and the front-pins can either
dangle around in an uncontrolled way or sink into the PET as shown HERE in another K-30 with the fake Lenovo Solenoid.


Photo 2: Shows what settings I used for the video, i.e. Pentax DA 35mm/f2,4 wide open


AVI Video: (see attached file after the 2 photos!)

Very obvious: The solenoid does not actuate! The magnet is too strong!


HERE you can see the white Japan-Solenoid in action.

This is how it should be!
Attached Images
   
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File Type: avi AVI.avi (1.40 MB, 15 views)

Last edited by photogem; 12-08-2023 at 12:21 PM.
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