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01-26-2020, 05:08 AM   #1
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Detection of aperture block/diaphragm-block failure/stuck solenoid K-30, K-50, K500

How to detect aperture block failure on Pentax K-30/50/500


This is a step-by-step tutorial on how to identify the dark-exposure-problem on your Pentax K-30, K-50 and K-500.
All those use the green made in China solenoid for aperture control.
If the aperture control (diaphragm control) doesn't work any more, then in almost all cases the solenoid driving the aperture control is stuck.

This problem started with the introduction of the Pentax K-30. If you want to know more about details and the history,
read here: History of Solenoid



Method 1 with kit-lens or any other AF-lens without A-ring:
(such as DA 18-55, DA 18-50,DA50, DA35 many Sigma/Tamron lenses etc.)

a) Set the top dial of your K30/50/500 to AV-mode:



b) Set aperture "wide open":

for example: - DA 18-55: f3,5 (at 18mm) -- DA 18-50: f4,0 (at 18mm) - DA 50: f1,8 - DA 35: f2,4



c) Take a photo:


This photo should be dark/underexposed!



Next step:


d) Set aperture "full stopped down" for your given lens:

for example: -DA 18-55: f38 - DA 18-50: f36 - DA 50/DA35: f22


e) Take a photo(if necessary use the flash if daylight isn't bright enough):


This photo should be fine!




The test shows you that the solenoid doesn't need to actuate when the lens is fully stopped down, that's why this photo is alright!
But with the lens wide open the solenoid has to actuate but can't because it is stuck.

If you done the test this way, you can say with 99,9% certainty, that the solenoid is stuck and needs to be replaced.


Method 2: Using Live-View mode with any A or AF lens with or without A-Ring:
(such as DA, DA-L, FA, F or A and those of other manufacturers with A-ring)

If you use a lens with an A-Ring set it on A!

This is best done with a prime lens, such as DA50/2,4, DA35/2,4, F/FA50/1,7/1,4
or any other which allows a good view into the front of the lens to see the aperture blades.

This photo shows the F50/1,7 set on A:




a) Set the mode-dial to any mode such as AV, TV, TAV or P:

b) Turn your K-30/50/500 (switched ON) so you can see into the front of the lens!

c) Now press the Live-View button:


If the aperture in your lens moves to f4, the solenoid works alright:






But if the aperture is fully closed,
the solenoid is stuck and damaged:






Often (but not always!) you can still take photos in LV (Live-View), while photos taken through the OVF (Optical-View-Finder) are underexposed! This is due to the solenoid actuating twice plus the important fact that the mirror is up as soon you activate LV!
This drains more power (mA) from the battery (has nothing to do with voltage which I will explain later).
As soon as you press the shutter-release-button, the mirror goes down and this sudden stop of holding the mirror up allows some extra power and thus the solenoid often (but now always) now actuates this second time. But because the solenoid was stuck the first time metering was not perfect. Metering was done full stopped down instead of f4,0! So you get some kind of alright photo but it isn't really correct!

You cannot you check the function of the solenoid in M-Mode and preselect aperture!
In M-Mode the solenoid is not used by the camera!


But all the other parts of the complex aperture control mechanism are used, this is the reason why manual lenses and green button metering does work.


With the Pentax K30/50/500 open you can check this easily:
As soon as you have disassembled your Pentax you close the flash (otherwise the flash capacitor will charge, danger of receiveing a shock as explained here, plug a lens on and insert the battery: Do the tests in AV/TAV and then M-Mode and you can see the difference. Of course if the solenoid is stuck you can see it just doesn't actuate at all except possibly in Live-View-Mode, but as soon as you have exchanged the solenoid for the white Japan-made solenoid, you can do the testing.

Of course in most cases this will also work if you apply the filing/sanding-method but why you better stay away from this you can read here:
Why you shouldn't file/sand the plunger of the green China-solenoid but replace it


Any discussion, commentaries etc. please post here:
Dark exposure problems on K-30 or K-50? Discussion Thread - PentaxForums.com

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a-ring, aperture, control, da, dark images, k-30, k-50, k-500, lens, m-mode, pentax, pentax k-30, pentax k30, pentax k50, photo, solenoid
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