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 analoge *ist). It looks identical to those used in the later DSLR bodies and had almost the same impedance. But its holding-force and body thickness was slightly different. Some which I and others had found had opposite polarity as well but others applied it with success in DSLR bodies, so it looks like that there were different versions used. Another type of solenoid was used as well for example in the Pentax MZ5/n. But Pentax didn't keep it up later on. This solenoid was driven with 6VDC (rated with 4,5VDC) by the solenoid-driver, impuls was 6.45V.

3. 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). It looks almost similar to the DSLR solenoids but aside of a tiny differenz in bobbin-size it has a slightly different holding force and often me and others have found polarisation to be opposite to the later introduced DSLR solenoid.

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


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 was Shinmei, Japan... also manufacturing similar solenoids for ALPS and Matsushita.


The next drawing shows that this new introduced Japan solenoid for DSLR bodies had now 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 new DSLR-solenoid made in Japan (also for ALPS) It had a live-timespan of remarkable 100.000 actuations!


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


When Shinmei moved production to China, difficulties started!

The material of the body changed to green colourand instead of using PTFE (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 tried in the flash circuit of the Pentax K100D, K100D, K200D, K-m, K-x and K-r but as far as I know mainly in those delivered to Europe.
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 do 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, which some mistake for a resistor or chip-resistor. This diode looks almost identical to an SMD-resistor, and yes, it resists into one direction (infinite ohms) but not into the other (zero ohms)
Nevertheless, it is a good idea to resist such chips were you don't want them or were they just don't belong to.

Some repairshops quote that they exchanged a chip-resistor but following the circuit very closely I just could not find any. It wouldn't make sense either, because if one studies the curve and quick response the solenoid has to actuate, any resistor would basically block any quick response. The solenoid does depend mainly on "surge-power", i.e. milli-amperes delivered quickly and not on voltage. If one studies the curve, one can quickly find out, that there is a range which is best for minimum holding-force. I challenge anybody who insists on some chip-resistor to prove it to me. I am curious for the outcome. And should I be wrong, I will happily "throw my hat" on the ground and apologize!


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:



But this change turned out to be the beginning of difficulties, due to several reasons described here as well:

The plunger of this solenoid often remained closed/stuck! The diaphragm/blades/aperture of the lens could not open and this led what is now often called ABF = "Aperture-Block-Failure", "dark-image-syndrom", "dark-exposure-problems" etc.

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. The made in Japan solenoid was no longer available, machines were already since a long time in China, the plants in Japan closed, so no chance to go back to this Japan-made solenoid!


Some early KS-1's, K-S2's and many K-50's as well of course K-500's still used the earlier China-made green solenoid and thus some of them failed and still do fail.

It is mainly due to fact that the metal body + plunger of the China-Solenoid is made out of relatively higher coercivity material, i.e. it retains its magnetism after the field strength is removed!


This 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.

Combined use of the AA-Adapter with rechargeable AA-batteries (best are Eneloops) + regular use has proven as the best way to avoid ABF.

I know of (very few) cases were this is the case. Usually high-shuttercount + ABF indicates non-use for some time.
But not always, I have encountered cases, were ABF just happened the next day.



But good enough: As far as I can tell the green solenoid now used in the Pentax K-70 is superior to the early version!
And yet: The holding force is still stronger, it does not fire as quick as the white made in Japan-Solenoid!

Close-up photos of the solenoid used in the K-70 show a very nicely machined plunger with a very smooth 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.

Beware of those green China-Solenoids now being sold on ebay, aliexpress and other sources,
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! They have again a way too strong holding force, also because they have a longer and thus stronger permanent magnet!
They were constructed for a very simple "press-button-open-tray" circuit

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.

- Beware also of blue-coloured China-Solenoids from ROM-Drives:
Wrong impedance (15ohms)! Danger of exodus for the "solenoid-driver".

- Again: Beware of green solenoids which are filed/sanded!
Further information why you should avoid this you can study HERE

- Beware using white Japan-made SLR solenoids from some MZ/ZX SLR-bodies!
Recently I did a vice-versa test by inserting the China-made green solenoids into a MZ50, MZ7 and MZ30.
They didn't work at all!

Some companies offer modifications "in weight, structure and/or surface", sounds impressive, but if you study such a modified solenoid:
They are just filed, which of course alters weight, structure and surface!


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:

GOOD NEWS (for the latest green China-solenoid used now in the K-70 and for repair:

I don't know when Ricoh demanded of their manufacturer another very good modification.


They changed the size of the magnet, it is shorter and thus has less magnetic power:



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


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

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

3. The 2.nd Modification: Same alloy as in the 1.st modification but even shorter magnet.



And as can clearly be seen: The solenoid on the Lenovo (fake Pentax) solenoid on the right has a larger magnet
Worse than Version-1, i.e. the original non-modified China-solenoid.

[normhead]

Cool stuff. Great pictures.

[skolkmeier]

Cool stuff. Great pictures.

My ks2 was manufactured in May of 2017, and it failed as well.

[niels hansen]

That is a true horor story. it shows a firm with very little quality control and a bad morale. A decent firm had taken hands on the problem, stopped using and given free exchange of the green soleonid.
I have a K30 with problems and a KP. My first KP was replaced after a few months.. The actual KP is good - hope it lasts - if you can overlook the imprecise pdaf.
Following several threads I now know that I am asking for too much of the pdaf.
BUT my impression is that the rate of succes was better on the K 30.
Together with a freind we have tested the rate of succes on his Nikon 800. It was not impressing either.
I dont know if the Pentax morale is worse than other firms- I doubt. The factories make cameras for the shareholders, not the photographers.
I love and use the m 42 Pentaxes

[StiffLegged]

The factories make cameras for the shareholders, not the photographers.

And the May 2020 award for barmy business commentary goes to the above quote.

[reh321]

That is a true horor story. it shows a firm with very little quality control and a bad morale. A decent firm had taken hands on the problem, stopped using and given free exchange of the green soleonid.
I have a K30 with problems and a KP. My first KP was replaced after a few months.. The actual KP is good - hope it lasts - if you can overlook the imprecise pdaf.
Following several threads I now know that I am asking for too much of the pdaf.
BUT my impression is that the rate of succes was better on the K 30.
Together with a freind we have tested the rate of succes on his Nikon 800. It was not impressing either.
I dont know if the Pentax morale is worse than other firms- I doubt. The factories make cameras for the shareholders, not the photographers.
I love and use the m 42 Pentaxes

This is a very bald comment.

What do you mean by "success"?
What were symptoms of the first KP?
Was the first KP replaced under warranty??
What does your experience with a KP have to do with these words about the solenoid???

[photogem]

That is a true horor story. it shows a firm with very little quality control and a bad morale.

Not so easy, but it is very easy to judge:
As I wrote in my first post, the green China solenoid was tested for several years in the K100D, K110D, K200D, Km, Kx and Kr.
But only in the flash circuit, maybe because exchanging it if it would fail would be easier and faster than the one used for aperture control.
It never failed there!

So they felt it would be save to use it for aperture control as well because stock of the Japan-Solenoid was running short.

It was only after about 1 year when the first faults turned up, often under warranty, so one hardly heard of the problem.
Then it was said that the complete diaphragm-control-board was replaced, I heard different, i.e. they just replaced the camera, because exchanging the diaphragm-control-unit takes many hours to do so, it is more work than to replace the sensor! When we had the K5 sensor stains, as far as I know Pentax replaced the complete camera on warranty!


I have disassembled a K30 once to replace this unit, the steps can be studied here at the end of my first post
That's why I am also very weary when people tell me they disassembled their Pentax completly to get to this unit.

Anyway, the rest is explained in my first post in this thread and in many countries Ricoh did offer good solutions outside warranty times. Not always but hell.... there are similar stories of 1001+ other companies.

[niels hansen]

StiffLegged
My point is that companies primare goal is profit, costumer care is executied if it is profitable in the long run. The companies are not interested in the costumers, they are interested in our money.

reh321

I Mean the rate of af presicion.

My first KP was the first in Denmark, it came from Sweden I bought it because the K30 became unrealibel, did not know of the solenoid problems.
The problems were AF and batterilife. The camera was sent to Holland and was replaced under warrenty.
My experience with tke KP is not directly correlated to the soleonid scandale. It is reflections about the quality of Pentax - and probably others.
Cameras today are very sophisticated, maybe they are not sufficiently tested before launched
For the moment I am satsified witth the KP, exept the performence when taking spontaneous portraits of kids, where reliabel AF is essentiel. Being 77 years old MF is not realistic with the KP
BUT my experience with two defective Pentax Dslrs make me nervous. Will other problems occur - and when?
Talking with my freinds indicate that other brands are not better.
The Spotmatc from 68 is my lifebelt Two years ago it got a CLA.

photogem
Your article is splendid, but you write that Pentax felt that the green solenoid was good enough to use in another way.
Feelings are not testing. carefull testing under relevant conditions is a must. You dont test Wellingtons in Sahara

Perhaps my bgigest mistake was going digital. For the investment I could have bought tons of film and so on.
I hope that my english is good enough in this case

[photogem]

photogem
Your article is splendid, but you write that Pentax felt that the green solenoid was good enough to use in another way.
Feelings are not testing. carefull testing under relevant conditions is a must. You dont test Wellingtons in Sahara

Perhaps my bgigest mistake was going digital. For the investment I could have bought tons of film and so on.
I hope that my english is good enough in this case

Your English can be understood well enough, don't worry about it.
Funny enough you wrote something which you mean differently, but luckily one cannot test/measure "feelings"!
It would be terrible if one could. One can only feel them if one has them.


Anyway: If you would be able to understand Japan, business over there, rules etc. and.... the importance of beer behind the scene (I am not kidding)
then you could see that actually it is quite a hard road for Ricoh and was more so with Pentax (has nothing to do with Asahi-beer or Ashahi which is just a name and means morning sun). I can't find this post anymore here in the forum, but a member once explained it pretty well.

Yes, business these days has changed a lot but the world has changed a lot. I am for finding solutions because it is so easy to fall for the Don Quijote trap... i.e. fighting what cannot be fought. Way to large for us.

So you have a great camera with your KP, it is not perfect, maybe ask the necessary questions with examples in the KP threads?
I sometimes love to take photos of birds and since I have the 55-300PLM I find AF with my KP very good but I am not the person to ask,
birds and moving objects never were that important for me.


If you still have your K30, then maybe repair it or get it repaired and then you have the AF you liked?
The K30 even can drive the KAF4 lenses with the 1.10 firmware!
I personally liked the AF of my K5IIs the most and found it the most ridicilous that Ricoh never offered a firmware update for KAF4 for the great K5 series. The K5 already is in some ways superior to the K30/50 and the the K5II for sure. Not to support those was a big big mistake because many customers found that too mean and stopped buying the new Pentax bodies, either stayed with their K5-series or ... sadly... swapped company.

[reh321]

I Mean the rate of af presicion.

My first KP was the first in Denmark, it came from Sweden I bought it because the K30 became unrealibel, did not know of the solenoid problems.
The problems were AF and batterilife. The camera was sent to Holland and was replaced under warrenty.
My experience with tke KP is not directly correlated to the soleonid scandale. It is reflections about the quality of Pentax - and probably others.
Cameras today are very sophisticated, maybe they are not sufficiently tested before launched
For the moment I am satsified witth the KP, exept the performence when taking spontaneous portraits of kids, where reliabel AF is essentiel. Being 77 years old MF is not realistic with the KP
BUT my experience with two defective Pentax Dslrs make me nervous. Will other problems occur - and when?
Talking with my freinds indicate that other brands are not better.
The Spotmatc from 68 is my lifebelt Two years ago it got a CLA.

What lenses are you using and how much do you depend on "isolation"?

Our daughters were born when I was in my early 30's - at a point when I was using my "Super Program", a manually focused camera. Honestly, I would have had a hard time focusing on them perfectly; little kids, especially our younger daughter, just move too fast, but I have always taken pictures with a "comfortable DOF" .... often an f-stop around f/8. Today I have a KP, which I almost always use with one of three lenses - a Sigma 10-20mm, a DA 18-135mm DC, and a DA 55-300mm PLM; you will notice that the latter two have in-lens focus motor, which I greatly prefer. I almost always use my KP around f/5.6 - f/11 also, and the pictures I take with that camera are always in focus - in 18 months I have never taken a photo with my KP that is out of focus. In general, I am extremely happy with my KP - I have no complaints of the quality that Pentax has put into that camera, so I am completely confused by your complaints.

BTW - the KP has less battery life than the K-3ii does, but everyone knows that - it has the same smaller battery that the K-50 does, but that has never been an issue for me, either the K-30 or the KP.

[photogem]

I think this belongs now into a KP or different thread.
The KP doesn't use a solenoid but a stepper-motor.

[clackers]

.. The actual KP is good - hope it lasts - if you can overlook the imprecise pdaf.

?

There should be no problem.

Have you done the microadjustments? If they require more than -10 or +10 you need to send the body back, its AF module is out of alignment.

[reh321]

My ks2 was manufactured in May of 2017, and it failed as well.

As failing versions of the K-30 were returned for warranty service, Pentax realized they had a problem, and the modified design resulted. By this time, the K-S2 was ready for production. This design apparently was better, but the "green" solenoid was still a weak area, so some K-S2 and K-70 models still fail. Since this is a problem with aging, dealing with it is not easy, so I believe Pentax should just give up on it and use the stepper-motor based design on future cameras.

[niels hansen]

Just returned fro a sailing trip in my nordic folkboat without connection to the shore, I will thank for the answers.
photogem:
my daughter has lived in Japan for two years, I visited her and her impression was very much like yours, not always sympathetic. I have been in KP threads, and my conclusion is that I ask for too much concerning pdaf. . A repair of the K30 is practically impossible in Denmark, and I am afraid of doing it myself, even with help from the eccelent from k30 threads. I use it manually with m 42 lenses
reh 321
My lenses are: Sigma 10 -20, DA 35 f 2,4, Da 50 f 1,8, Sigma 70 f 2,8 macro and Tamron 70 - 300 macro. In portraits i prefer shallow DOF and thats where the pdaf not always is precise. When I use the smaller f stops like you do there is no problem.
The battery life with the Kp that was replaced under warrenty wafar below 100 poses without flash and LW
Clackers
All lenses are fine tuned. I have a resolution chart, takes a photo in live view and find the fine tune value that gives the same result as live view. It works fine.
Finally some reflections between the folkboat and Spotmatic.
The folkboat was designed in 1941, newer designs are bigger, faster and more comfortable, but when it comes to the handling in especially hard weather it is still second to none, it is a surviver . In a way I think the same about the old all metal cameras, like the spotmatic.
I forgot: one of the virtues of the KP is the eccelent exposure. I use the KP instead of my Spotmeter for analogue BW

[photogem]

@photogem:
my daughter has lived in Japan for two years, I visited her and her impression was very much like yours, not always sympathetic.

Oh... but isn't nor was it my impression of the Japanese mentality at all!
I have met quite a few Japanese businessmen and usually met an amazing code of honor, a true sense of doing things right.

[photogem]

New information added, but I am going to have this thread moved to the articles forum:
Pentax Articles | Pentax K-1 | Pentax K-5 | Pentax K-30 - PentaxForums.com
This thread is not only K30/50 related but for all Pentax bodies using a solenoid for aperture-control