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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 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 "aperture problem", "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.


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 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.



With the introduction of the Pentax K7 Pentax developed a new design, using a robust stepper-motor instead of a solenoid.
This design was used until now in the following DSLR Pentax: K7, K5, K3, KP, K1 and also in the K-01. HERE you can see it in the K-01.

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 too strong holding force.
They were constructed for a very simple "press-button-open-tray" circuit.


Beware also of blue-coloured China-Solenoids from ROM-Drives:
Wrong impedance (15ohms)! Danger of serious damage of the powersupply which is a socalled "solenoid-driver".

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


Some companies offer modifications "in weight, structure and/or surface"
Well, if you sand of file, you change all three aspects of course.
But that's not the solution, to me more of a disimprovement




Last edited by photogem; 02-28-2021 at 03:56 AM. Reason: New info added by Photogem
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09-20-2020, 10:19 AM - 2 Likes   #31
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Your history of the selenoids used in Pentax bodies is a real gem, photogem.

Using low-quality selenoids in a succession of entry-to-midrange bodies, even after they must have understood the issues, remains one of the biggest Pentax fails. In my book, it is right up there with the notorious first-generation SDM failures. The latter has ultimately kept me from investing in a single early-SDM lens, and the former makes me dread the day when I may have to explain to my wife why the K-70 I so warmly recommended to her has taken to produce black images. (Knock on wood, so far it has been working great.)

Now, humans are bound to make mistakes, and I understand the need to find cost-effective solutions when you have to run a successful business. But, to my mind, one of the key takeaways from the selenoid story is how hard it can be to rectify going cheap once you've gone down into that rabbit hole, even when it starts to dawn on you that you've made a serious mistake. Even when Ricoh understood what was going on, it seems they concluded they would just use a somewhat better, yet still possibly-inferior selenoid (compared to the no-longer-available Japan model) for the K-70. However, consumer trust is also a kind of capital, one that is hard to restore and one that shouldn't be squandered for perceived short-term benefits. Having the first Pentax DSLR body they ever tried fail on them just after the warranty period had ended may have driven many a beginner away from the brand before they became more deeply invested in the system, which would be a shame.

(End of rant. You guys know how much I love Pentax digital for all the things it has done right.)


Last edited by Madaboutpix; 09-20-2020 at 11:29 AM. Reason: More nuance.
09-20-2020, 11:28 AM - 2 Likes   #32
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Ah... but you see, they didn't know really. They knew the solenoid was different, possibly they knew it was now made in China.
But they tested the solenoid in the more simple circuit of the K100D, K200D, K110D, K-m, K-x and K-r.
So quite a few years without any failure.

When the first failures appeared with the K30, nobody knew then.
It was the Russians finding out first applying the soldering method and it was shedding light into what had to come.
The dreaded sanding method appeared but soon proved to be wrong.

I have the latest K70 solenoid right here on my workbench and it is even better then the one from my first K70.
I purchased this late K70 because it was repaired and failed again.
So just today I had the chance to search for this mysterious resistor-chip, well, I could not find any!


But I managed to resist chips,
but some need to be more careful

During the next week I will meet the son of the most experienced electrical engineer I ever met in my life, he himself is now a master of electronics as well, his dad sadly left this planet few years ago. With him I will study the circuit any further just to make sure I didn't miss anything but I think I didn't.

Last edited by photogem; 09-20-2020 at 11:03 PM.
09-20-2020, 11:50 AM - 1 Like   #33
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QuoteOriginally posted by photogem Quote
Ah... but you see, they didn't know really. They knew the solenoid was different, possibly they knew it was now made in China.But they tested the solenoid in the more simple circuit of the K100D, K200D, K110D, K-m, K-x and K-r. So quite a few years without any failure.

When the first failures appeared with the K30, nobody new then. It was the Russians finding out first applying the soldering method and it was shedding light into what had to come. The dreaded sanding method appeared but soon proved to be wrong.

I have the latest K70 solenoid right here on my workbench and it is even better then the one from my first K70.I purchased this late K70 because it was repaired and failed again. So just today I had the chance to search for this mysterious resistor-chip, well, I could not find any!

But I managed to resist chips,but some need to be more careful.

During the next week I will meet the son of the most experienced electrical engineer I ever met in my life, he himself is now a master of electronics as well, his dad sadly left this planet few years ago. With him I will study the circuit any further just to make sure I didn't miss anything which I daubt.

Well, I would be willing to give them the benefit of the doubt then. But still, given that they made the K-70 so nice in so many other respects, I wish they had just let the tried-and-tested stepper motor trickle down to it too. Would it really have made the K-70 so much more expensive than the competition?

I know I'm probably suggesting this in hindsight. And they do deserve some credit for trying to source even better selenoids for later K-70s.

I just hope the right people at Ricoh will read all the commendable research you have accumulated. You're a real asset for the brand, photogem.
09-20-2020, 11:01 PM - 3 Likes   #34
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QuoteOriginally posted by Madaboutpix Quote
Well, I would be willing to give them the benefit of the doubt then. But still, given that they made the K-70 so nice in so many other respects, I wish they had just let the tried-and-tested stepper motor trickle down to it too.
This would have made the K-70 larger.
The K-S1 was a unique design because of not giving up the K-design.
Other companies changed their mount: Vintage lenses could not be used anymore. Not so with Pentax! But the K-S1 was not that well received aside of Japan.

In Japan they were rightly very proud of it. But this is also linked to the fact, that many Japanese have smaller hands and fingers! For those the K-S1 was a revelation.
Impossible to achieve with a stepper-motor. What happens if you you a stepper-motor and yet want to keep it small could be seen with the K-01. It was similar in size as the K-S1 but kind of castrated.


So the K-S2 and then the K-70 (99,5% identical body) were an attempt to keep it small as possible plus WR + flip-screen Plus amazing other extras such as pixel-shift.
Impossible to achieve for that price and size with a stepper-motor!

QuoteOriginally posted by Madaboutpix Quote
Would it really have made the K-70 so much more expensive than the competition?
Not only more expensive but larger!

QuoteOriginally posted by Madaboutpix Quote
I know I'm probably suggesting this in hindsight. And they do deserve some credit for trying to source even better solenoids for later K-70s
.
I do think that from that moment on when they 'got it' that it was just and only the solenoid, everything was done to solve it. It took time though. And some still insist that it must be more than the solenoid (Ant & Bee and the 'make-believe-rainbow') and try to fabricate something that never existed.
There is all evidence that is needed: The made in Japan solenoid never failed, i.e. is the evidence per se. Of course no forensic evidence, this ain't no crime!

Nothing more is needed. Nothing else failed ever than the made in China solenoid.


QuoteOriginally posted by Madaboutpix Quote
I just hope the right people at Ricoh will read all the commendable research you have accumulated. You're a real asset for the brand, photogem.
I guess there is like always the problem of different levels: Business/Advertising vs. Engineering vs. Form vs. Function etc.... maybe even the power of shareholders.
Different interests, different view-points, different education etc.
Ah.... I almost forgot: Stubbornness and ignorance! Don't know which was there first, kind of 'hen or egg'.

But there might be another problem: I call it the co-existence of the designer and the engineer.
A good designer is the person who can see into the future, has the idea, is the entrepreneur. He might even have quite some technical knowledge but he is not the person who can make it alive (the end-product). That is the work of the engineer.
In older days the engineer was as much respected, not so much these days anymore.
But they need to work well together, not so easy anymore when business-economists have the saying.
That's the modern problem: Business-economists are often very inexperienced about real live, juggle with figures and thus often have a very onesided/tilted view of reality.

09-21-2020, 05:44 AM   #35
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QuoteOriginally posted by Madaboutpix Quote
Well, I would be willing to give them the benefit of the doubt then. But still, given that they made the K-70 so nice in so many other respects, I wish they had just let the tried-and-tested stepper motor trickle down to it
I believe the solenoid was a “tried-and-tested design which had trickled down to it”; photogem’s history shows why the designers would think that way - all it needed was a simple tweak. Now they have shown that the “tweak” does not work reliably, so now it is time to give up on it.

Last edited by reh321; 09-21-2020 at 06:17 AM.
09-21-2020, 06:38 AM   #36
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There is no need to give up on the principal of the solenoid.
All.... really all that needs to be done is to get a Japan-Solenoid, send it in to the manufacturer with a sledge-hammer and ask the manufacturer to find a magnet which holds the plunger with exactly the same holding force as does the Japan solenoid. That would solve it.

Just this weekend I opened a K-70 of very recent manufacture....
It still had warranty and was repaired on warranty but failed again.
So a good chance to fish for chips (it was quite a resisting chip, seems to be a stealth chip


Anyway, the solenoid was even better than the previous one. Almost correct holding force.

So if you quote my words and particular and in this thread, do it correct please and don't misalign what I said!

Last edited by photogem; 09-22-2020 at 11:39 PM.
11-04-2020, 09:12 PM - 1 Like   #37
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QuoteOriginally posted by photogem Quote
With the introduction of the Pentax K7 Pentax developed a new design, using a robust stepper-motor instead of a solenoid.
This design was used until now in the following DSLR Pentax: K7, K5, K3, KP, K1 and also in the K-01. HERE you can see it in the K-01.
That actually explains why there is a lump to the left of the mount on the K-7/5/3 and prominently on the KP! Great work on this photogem!
12-26-2020, 10:31 AM - 1 Like   #38
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Thanks for everyone who posted here. I was having the same aperture issue with my K-X and decided to take a leap of faith and crack open the camera. I had ordered the "white solenoid" from Japan in the hope of finding the green one when I open the body. To my surprise, the K-X I have already had the white one.

And since there was no picture out there that clearly shows where exactly it sits, I took that picture below. You can now clearly see it as soon as the plastic body is removed. Tip: note down where screws go as there are about 5 different sizes.



Since the wires and solder dots are microscopic I did not yet want to replace the solenoid with another white one. What I ended up doing instead is remove the tape holding the wires, unscrew the solenoid in place and leave it wired. Once the solenoid is lose, you can pull it apart in two pieces, where the "bottom part with no screw" (left side of it, looking at the picture) can be removed and tapped on a table to remove some remnants of magnetic field. Then put everything back together.



Just doing this did the trick for me. I still have the spare white solenoid in case this small operation was not enough and I have to put the new one in place.

Attached Images
   
12-26-2020, 10:49 AM   #39
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Fascinating.
12-26-2020, 03:29 PM   #40
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QuoteOriginally posted by frankl Quote
Thanks for everyone who posted here. I was having the same aperture issue with my K-X and decided to take a leap of faith and crack open the camera. I had ordered the "white solenoid" from Japan in the hope of finding the green one when I open the body. To my surprise, the K-X I have already had the white one.
Well, you shouldn't be surprised to find the white Japan-Solenoid in your K-x because as I wrote it, the K-x was the last one which had it for sure and the K-r has it most times. ONLY in the flash-circuitry mainly sold to the EU one finds already the green China-solenoid, the Europeans where Ricoh's guinea-pigs.

Nevertheless, it would have been the first time ever that a white Japan-Solenoid failed and if it would be wrong (which I daubt) it should go wrong again very soon.

Tapping the solenoid parts on the table to remove remnants of the magnetic-field was never a solution for the green China-Solenoid ever!

It cannot work because when the Pentax is NOT IN USE the plunger is ALWAYS NEAR THE PERMANENT MAGNET and gets magnetized.
Thats the problem and the too strong holding force.

So if your solenoid or better if you K-x will continue to work then it was not the solenoid, that I know for sure.
12-27-2020, 08:17 AM - 1 Like   #41
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The K-X, so as mine, has a history of having battery issues. Normal batteries last few shots, while high voltage Eneloops or Lithium batteries last longer. So maybe my solenoid issue is in fact due to not enough voltage to move the solenoid off the magnet itself...
12-27-2020, 03:42 PM   #42
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QuoteOriginally posted by frankl Quote
The K-X, so as mine, has a history of having battery issues. Normal batteries last few shots, while high voltage Eneloops or Lithium batteries last longer. So maybe my solenoid issue is in fact due to not enough voltage to move the solenoid off the magnet itself...
That problem is solved very easely:
Battery type AA/NiMH/Eneloop in K-x, K-r, K30 K50, K500 as well as *ist/K100/200/2000 - PentaxForums.com

But it is not the voltage which is important, it is milli-amperes!
The surge-power.

But the holding-force of the Japan-Solenoid is very exact and never needed any manipulation.
the PTFE makes the plunger move much more easely, both those facts together with the alloy make all the difference.

I have seen white solenoids from Pentax DSLR bodies with very high shuttercount: Never any failure!
12-27-2020, 08:46 PM - 1 Like   #43
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QuoteOriginally posted by photogem Quote
There is no need to give up on the principal of the solenoid.
All.... really all that needs to be done is to get a Japan-Solenoid, send it in to the manufacturer with a sledge-hammer and ask the manufacturer to find a magnet which holds the plunger with exactly the same holding force as does the Japan solenoid. That would solve it.
................................

So if you quote my words and particular and in this thread, do it correct please and don't misalign what I said!
and use the same materials as used before the change.
12-27-2020, 09:58 PM - 1 Like   #44
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QuoteOriginally posted by reh321 Quote
and use the same materials as used before the change.
If I understand what photogem is saying correctly (and what you are saying), then when the company transferred production from Japan to China, it also abandoned the "Japan solenoid" Teflon design in favour of the presumably cheaper alternative, PET. If the Teflon variant is out of production, I wonder if Ricoh would be willing to purchase a sufficient volume to make it worth setting up the needed assembly line at the new plant.

Alternatively, wouldn't a better plan from Ricoh's perspective be to transfer all body tiers to the stepping motor?
12-28-2020, 08:59 AM   #45
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QuoteOriginally posted by Breakfastographer Quote
Alternatively, wouldn't a better plan from Ricoh's perspective be to transfer all body tiers to the stepping motor?
Not really:
Larger bodies, more weight and more expensive.
Read here what I wrote about this issue:
Buying a new camera body - Page 4 - PentaxForums.com
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