[JoseFF]

I have been looking at the aperture mechanism on a K-x (model I currently have with the covers off). It looks like the horseshoe solenoid referred to at the beginning of this thread is used to stop the aperture from closing down when the mirror motor is activated. I was experimenting using manual (M) mode and a long shutter time (in seconds).

If I set the aperture to the maximum value for the lens, the solenoid actuates immediately and the gear that drives the aperture lever does not turn when the mirror flips up. If I set a smaller aperture the solenoid activation looks to be delayed, and the gear turns part way to step the aperture down. Looking at the the photos of the aperture mechanism in the thread https://www.pentaxforums.com/forums/189-repairs-warranty-service/325334-k-30-...iy-repair.html it looks like the gear set include a rotation sensor (disc with holes in last photo) that could detect how far the aperture has opened. The lever may then be stopped at the required aperture by actuating the solenoid.

If the solenoid is sticking (or being held in place by magnetization of the core) it looks quite possible that the aperture would always close all the way down. Looking around the web, it appears the same basic design was also used back on the auto focus film cameras prior to the *ist D.

That could let us jump to the conclusion that changing or repairing the solenoid will fix the problem...

[nihonsuki]

Using the Russian photos and instructions translated by Igor, I successfully disassembled my K-30, overhauled the armature, and reassembled the camera. My camera was starting to suffer from the dreaded aperture block problem after having been repaired for the same problem 2 years ago. Just keep in mind that that there are different lengths and types of screws when taking the covers off. Also, there's a chromed screw deep inside the battery compartment which holds down the top cover, and another screw under the bottom cover which holds down the front cover. I'll wait and see if this solved the problem, but in any case, the repair is simple enough that I'll go in and modify the armature again if necessary. Many thanks to all who contributed to the solution!

[niceshot]

Using the Russian photos and instructions translated by Igor, I successfully disassembled my K-30, overhauled the armature, and reassembled the camera. My camera was starting to suffer from the dreaded aperture block problem after having been repaired for the same problem 2 years ago. Just keep in mind that that there are different lengths and types of screws when taking the covers off. Also, there's a chromed screw deep inside the battery compartment which holds down the top cover, and another screw under the bottom cover which holds down the front cover. I'll wait and see if this solved the problem, but in any case, the repair is simple enough that I'll go in and modify the armature again if necessary. Many thanks to all who contributed to the solution!

Keep us abreast of the situation , let us know if it indeed worked.

[nihonsuki]

I found the description of how this assembly works, the problem is how to translate it. The guy uses some physics jargon which I hardly understand in Russian

He says the following: "Описать действие узла я могу следующим образом:
В исходном состоянии рычаг управления диафрагмой притянут якорем в верхнем положении за счет поля постоянного магнита.
По приходу импульса на катушки эл.магнита создается магнитное поле, противодействующее полю постоянного магнита, вследствие чего
общая напряженность магнитного поля становится близкой к нулю.
Под действием пружины (рычаг управления диафрагмой подпружинен, и стремится вытащить якорь из каркаса катушек)
рычаг управления диафрагмой вместе с якорем уходит вниз и творит свое доброе дело. (не видно).
Начинают вращатся шестерни, которые после окончания импульса, через некоторое время возвращают рычаг с якорем в исходное состояние каким то толкателем.
Толкатель на шестерне проворачивается дальше и освобождает рычаг для следующего хода, шестерни останавливаются в исходном положении.
Рычаг с якорем удерживается магнитным полем постоянного магита и опять стремится выдернуть якорь и так по новой."

"I can describe the way this assembly works in the following manner. Initially, the arm that moves the aperture is held in the upper position by the electromagnetic field created by the magnet. Once the electric impulse reaches the coil, an electromagnetic field opposite to the current of the magnet is generated, the result of which is that the total electromagnetic field strength is close to zero. The arm that moves the aperture is spring loaded, which pulls it down to open the aperture. The cogs start spinning and when the electric impulse is gone, they return the arm that drives aperture into the initial position using a pin. The pin on the cog moves further and frees the arm that drives the aperture for the next actuation. The cogs return to the initial position and the arm that drives the aperture as well as the armature are held by the electromagnetic field generated by the magnet."

Sorry - haven't done physics in 20 years or so

What I don't understand is how this results in underexposed pictures. The aperture is normally fully open, spring loaded when the lens is twisted into the mount. Doesn't the solenoid allow the aperture to start closing? If the armature sticks, wouldn't this tend to keep the aperture open?

[nihonsuki]

Keep us abreast of the situation , let us know if it indeed worked.

First shot of the day this morning was not underexposed! I have not seen any underexposed shots since I overhauled the solenoid yesterday. Looks like the problem has been fixed!

[niceshot]

First shot of the day this morning was not underexposed! I have not seen any underexposed shots since I overhauled the solenoid yesterday. Looks like the problem has been fixed!

good deal

[ekip]

Using the Russian photos and instructions translated by Igor, I successfully disassembled my K-30, overhauled the armature, and reassembled the camera. My camera was starting to suffer from the dreaded aperture block problem after having been repaired for the same problem 2 years ago. Just keep in mind that that there are different lengths and types of screws when taking the covers off. Also, there's a chromed screw deep inside the battery compartment which holds down the top cover, and another screw under the bottom cover which holds down the front cover. I'll wait and see if this solved the problem, but in any case, the repair is simple enough that I'll go in and modify the armature again if necessary. Many thanks to all who contributed to the solution!

What exactly did you do to the armature to fix the problem?

Thanks

[HarisF1]

I tried to sort out my k-30 by grinding the two arms on the horseshoe piece down using sandpaper. A change of one millimetre made no difference. Sanding it down by around 1.5mm allowed the lens to work wide-open, but not stopped down. It's also caused a bigger issue. The mirror keeps flapping and so autofocus out of liveview doesn't work. The images also come out rather blurry.

The reason this change happened is because the arm is now too small to be attracted to the magnet which means the mirror and aperture control mechanism works without any 'control'. Not a good solution.

It looks as though there is an issue with the little lever that the armature controls. It seems like it isn't moving freely as it should. I'd like to maybe open it up but it would take way too long.

I also tried to take the arm out of my working k100d and it made no difference, even when I sanded that one down too. I replaced the shortened part back into the k100d and it still works perfectly, thank God!

I might try to glue the arm in place so that the mirror flap issue can stop. At least then I will be able to use manual aperture lenses.


I hope my input can help someone find a fix for their camera.

[athlonus]

Hi,

DSLR and Flash tech is here. I work on all major DSLR systems.

When compared to others, Pentax is a very competent and high quality brand. They just suffered from bad management and supply chain issues since Hoya ownership. We will see how Ricoh would do.

Anyways...

I have been reading the posts and only a few have a clue on what the issue is.

First, the part called 'solenoid plunger' is defective. It is out of voltage specs, requiring more power (than normal plungers used in older models) to disengage and let the main metal aperture gear which runs inside an optocoupler to stop on time. When it does not release the horsehoe aperture gear has nothing to be stopped by and goes all the way down (i.e. F22)

If you sand or modify the plunger, it will very likely to stop disengaging since it is very delicate. The Russian method is wrong, DSLR are not make like Ladas.

The official solution is to replace the plunger with a good one from older models. It is a very hard to find part but you can use some donors.

On the other hand, K-1.K-3, K-5 and K-7 systems are entirely different. There is only one step motor to control the aperture and they are less likely to fail.

As far as I see, K-x (K-m), K-r and newer entry level models use solenoid controlled aperture block only and whenever there is a bad batch of solenoid plunger inside it will stop in the early life of the camera.

Good day to all!

[athlonus]

Normally it should not make any difference due to the voltage regulator IC, however the plunger is very sensitive to small voltage variations, I need to hook up my scope and read the values with different power cells.

Another fix would be increasing the tension on the counter spring of the arm attached to the plunger's horseshoe. I have not tried indeed.

[HarisF1]

Someone mentioned that this part is also found in DVD players and other such devices. Can anyone else verify this? If we could buy a donor DVD player for £10 that would turn out a whole lot cheaper than buying a £40 camera body.

In my experience, the solenoid would not release the horseshoe at all, even when I sanded the edges down. At the point where it did release (due to sanding all too much), it would not recapture the magnetism leading to shutter flapping and loss of aperture control.

[athlonus]

Someone mentioned that this part is also found in DVD players and other such devices. Can anyone else verify this? If we could buy a donor DVD player for £10 that would turn out a whole lot cheaper than buying a £40 camera body.

In my experience, the solenoid would not release the horseshoe at all, even when I sanded the edges down. At the point where it did release (due to sanding all too much), it would not recapture the magnetism leading to shutter flapping and loss of aperture control.

I would first verify to get momentary voltage to the solenoid, camera body should send the power at a fraction of a second. In some cases, the solenoid coil becomes defective and could not demagnetize against the permanent magnet.


Then your best bet is old walkmans which use logic touch drive instead of direct mechanical click buttons. Those types almost all have the same part with the same size and specs. Before buying a walkman you should make sure it has the part (usually contains one) by looking at the PDF service manual, in the exploded parts view.

[JoseFF]

I would first verify to get momentary voltage to the solenoid, camera body should send the power at a fraction of a second. In some cases, the solenoid coil becomes defective and could not demagnetize against the permanent magnet.


Then your best bet is old walkmans which use logic touch drive instead of direct mechanical click buttons. Those types almost all have the same part with the same size and specs. Before buying a walkman you should make sure it has the part (usually contains one) by looking at the PDF service manual, in the exploded parts view.

Could you please tell us what old pentax camera models use the exact solenoid that could replace the faulty one in K-30 and K-50?

[athlonus]

For sure *ist, K-X, K-R, K10D models have two useful identical solenoids, one for the flash pop up up and the other for the aperture control. I have not checked any film SLRs but they (which were produced since 90's) are very likely to use the same part.

[niceshot]

For sure *ist, K-X, K-R, K10D models have two useful identical solenoids, one for the flash pop up up and the other for the aperture control. I have not checked any film SLRs but they (which were produced since 90's) are very likely to use the same part.

that is correct