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06-16-2019, 06:52 AM   #1
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Why you shouldn't file/sand the plunger of the green Chinasolenoid but replace it

Often people recommend filing/sanding/grinding the plunger of the green China-solenoid which is supposed to do the trick.

For some this method worked, at least for a while, but for others it didn't and there can be further consequences applying this method which can lead to complete failure of the "diaphragm-control-unit"

The reasons for this isn't just the plunger itself which gets filed/sanded but it is a combination of other facts!

I had done a comparison of

- the latest solenoid of a K-70
- the latest solenoid used for official repair of a K-30 (which failed again due to failure of the solenoid)
- the solenoids of a K-S1 and K-S2
- a green China solenoid with special etched plunger done by an official repairplace in Germany
(this failed as well just shortly after the 1 year warranty)

and
- the well regarded well regarded white made in Japan-Solenoid

You find the results HERE

It shows the steps Ricoh implied for solving the solenoid problem and it also shows why still some K-S1's and K-S2's and very few K-70's did fail and what could be done to solve this finally.

But back to the filing method:

Me (and many others) have tried this method several times. There is no question that it works because you do change the holding force.

But there is a difference how the solenoid switches now!
The complete diaphragm control mechanism is by itself a very special and clever mechanism.
Normally it has to be aligned. If parts go out of alignement, new alignement is quite complicated.

I have experienced 3 x K-30's with filed green solenoids where the diaphragm-control-unit afterwards went out of alignement.
This is due to the fact, that the plunger moves less accurate, more sloppy. I have uploades photos to show this in the manual for replacing the solenoid in the K-30 .

You can even hear the difference just by listening to the switch-sound of a K-30 with the original "white made in Japan solenoid" compared to those with either soldered plunger of those with a filed plunger.


The reason for this:

The white PTFE body (teflon!) as well as the green PET body act as a bearing for the plunger!
The green PET material is inferior to the more expensive PTFE.
The plunger has anyway some allowence for a slight tilt/movement due to the oval hole which sits on the lever but filed/sanded this movement becomes more sloppy.
This you also notice with the K-30 in use! With the prober white Japan-Solenoid it fires faster:

Necessary force to pull the plunger:
100g (0,98N) (the strongest ever 120g) Japan Solenoid
200g (1,96N) (strongest ever 250g) China Solenoid

With a powersupply based on a simple microcontrollerboard one can test how quick the solenoids releases.
Tested with 7.2V from the orig. Pentax Li-Ion battery D-LI109:

Releasetime Japan Solenoid: 10ms (and it still functions with an shorter impuls of 4ms!)
Releasetime China Solenoid: 100ms! It won't function at all with 10ms, forget 4ms.


But if one runs the China-Solenoid several times with 100ms/7,2 Volts and then tries with 10ms it does work 1x,
sometimes even 2x but then collapses back into its previous "stronger position", i.e. 100ms!

But worse: If one uses it many times with 100ms and then just lets it stand for a few hours it won't even once release anymore with 10ms but only 100ms!

Now changing over to AA-Eneloops instead of using the Li-Ion D-LI109 things do change:

The releasetime is now between 50ms for the Chinasolenoid and 8ms for the Japansolenoid, which even can at times be switched within just 2ms!


But there is another problem when filing the plunger.

The surface now can corrode and rust!
You can see this here as well as here

Now: You sure don't want rust particles in your K30 or K50 at all!

Aligning the diaphragm-control-mechanism is not easy, one has to know quite a bit to do this the correct way. The white solenoid was used with success in so many DSLR bodies and never failed in any repaired K-30 etc.! So if you make the effort and disassemble a K-30 or similar it is just better to play 100% safe and just use the white made in Japan solenoid. I don't think it makes sense to fiddle around and take risks which can lead to total damage.

Here 3 pages from the service-manual of the K-30 which show how to align the diaphragm-control-unit:
part1
part2
part3

Another problem which can result if this diaphragm-control-mechanism is no longer correctly aligned:
Stop-Down-Metering with the green button no longer works correctly!
This also can result if one just tries to force the green solenoid to work by applying serial shots, if the plunger of the solenoid all the sudden "snaps open" the force ... particular during serial shots... can be that strong that those complex interlinked toothed wheels get out of alignement together with this metal toothed wheel sitting in the optical sensor!

But the worst that can happen is that when the mechanism goes out of alignment and the spring which returns the white plastic wheel to its original position 'jumpes out' and not only stops any possibility for manual metering in M-Mode (because here the solenoid is not in use) but also it can block the wheel which then evidently will interfere with the mirror/shutter-release mechanism or even do damage to it!

The result is complete failure, here a photo of such an example:


You want to avoid this by all means because then your Pentax is pretty much beyond repair.
Alignement is impossible now. You have to replace the complete diaphragm-control-unit.



The steps to just get to the diaphragm-control-unit are as follows for the K30/K50:

1. Disassembly of the main body as shown in my tutorial for replacing the solenoid
2. Removal of TC100 Mainboard: Here you have to unsolder 19 wires
3. Removal of 0C000 SR-Block which itself cannot be disassembled, one needsto peel of special glue to access the screws
4. Removal of 0-A51 (Tripodplate)
5. Removal of T901 (Flex Circuit-Board with unsoldering 38 wires!)
6. Removal of T750 (Flash PC-Board: 7 wires + 11 lands to be unsoldered)
7. Removal of R4 (R-Plate)
8. Removal of T700 (Upper Relay Flex Board: 21 wires to be unsoldered)
9. Removal of A6 (G-Shoulder-plate)
10. Removal of 0-A010 (Front-Housing-Assembly, one has to know that this can only work if one applies 2V DC to G200 for mirror-up position!)
11. Removal of A13 (Battery-case and all related parts)
12. Now one has access to the diaphragm-control-unit!


During this procedure one can very easely "hurt" the 4 contact bushes of G8. These are the "male" part of G171 and as sensitive as the On/Off-Switch and a tiny bend of one of those bushes is almost impossible to correct back as the tension of those bushes comes into disorder. As with the On/Off-Switch it is then necessary to replace it with a new or good used one.


Here it is very interesting to note:
Those contact bushes never went out of alignement with the white Japan solenoid used in any of the pre K-30 Pentax DSLR bodies.
And many of those had very high shuttercount! Also they never went out of alignment if one swapped the Japan-Solenoid against the China-Solenoid. Misalignement happened only then, if one "tampered with the green solenoid", i.e. tried to make it work by modifying/meddling something, that better is to be replaced! If you have some bad material lets say for the sail of a sailboat, yes, you can meddle around, try to bungle/cobble... but there you know pretty well: It is messing around!


Last edited by photogem; 05-31-2020 at 03:23 AM.
10-25-2019, 05:39 AM   #2
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I have added the latest findings which resulted by doing further tests based on questions in this thread by member "Marktax" whose Pentax K-S2 had the stuck solenoid and later on didn't work anymore with OFV stop-down-metering/green button. He knows about another person having the same problem.
Also interesting what member "tonyzoc" experienced in this thread: He had his K-S2 repaired in California and it failed again and finally went out of alignment.


I checked OFV stop-down-metering on a K-50 and K-S2, both with "stuck solenoid".
The solenoid is not in action when using this method in Manual-Mode but:

If the solenoid either by applying serial-photos to let the plunger of the solenoid snap back or ... if filed:
This brings the complex mechanism of the diaphragm-control-block out of alignement, stop-down-metering is no more possible at all!
Then the complete diaphragm-control-block either needs to be aligned (very complex work) of the block needs to be replaced!
Replacing the solenoid (with the white Japan-version) is peanuts complared to replacing the complete block!

I have done it once and will not do it ever again! Way way to time consuming and and a feast for your nervous system, particular the sympathetic part (which then is not at all symphathetic to you anymore but quite the opposite)
See steps 1-12 in my main post.

Last edited by photogem; 05-31-2020 at 02:42 AM.
06-27-2020, 01:01 AM   #3
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My wife's K-30 only works normally using the LV, normal shots are over 5 EV underexposed. Any idea what's going on?!
06-27-2020, 01:11 AM   #4
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QuoteOriginally posted by Tord Quote
My wife's K-30 only works normally using the LV, normal shots are over 5 EV underexposed. Any idea what's going on?!
A typical sign for a stuck solenoid:
Often for quite a while it seems to work in LV normally, actually it ain't perfect:
When you have it switched on, turn in to look into the lens you can see that in the moment you switch to LV the aperture closes to the maximum of the lens while it should be f4,0! So metering is not exact but the photo turns out better, i.e. not underexposed.


Check HERE how to make sure it's the solenoid!


Last edited by photogem; 06-28-2020 at 12:35 AM.
06-27-2020, 03:22 AM   #5
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https://www.dpreview.com/forums/thread/4221791

This has improved things, if not 100%!

Last edited by Tord; 06-27-2020 at 03:41 AM.
06-27-2020, 04:20 AM   #6
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Temporarely with some risk of making things worse. If the solenoid is stuck and one uses force to free it, this acts onto all other components linked to it, it actually is a complicated mechanism. The problem is that then parts can go out of alignement.
The worst that has happened was that the complete diaphragm-control-unit has to be exachanged, you really don't want to undertake this work, it means unsoldering of about 32 wires, disconnect flexboards, many different screws, it is basically a complete disassembly of the whole camera. This undertaking might well be that you become a undertaker for your camera.

We had repeated cases where Pentax bodies repaired via filing/sanding by repairshops such as Pentax Camera Repairs PC35 Photolab went wrong:
https://www.pentaxforums.com/forums/184-pentax-k-s1-k-s2/399051-solenoid-pro...ml#post4851034 follow the thread and discussion.

Last edited by photogem; 09-26-2020 at 07:51 AM.
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