Pentax K-30 and K-50 have a problem with the aperture control block mechanism within the camera that causes them to not actuate the aperture, hence giving only black photos. This is due to a small solenoid within the camera, that over time becomes more magnetized and fails to actuate.

The fix is simple: take out the moving horseshoe part from the solenoid and then file or grind it down to reduce the magnetic force imposed on it at rest. The filing works because it reduces the effective contact area at rest, hence reducing the amount of magnetic flux lines going through it.

This post is an addendum to the very useful video posted here by MBS TV. This will show you how to open the camera and also a good technique on saving the screws.
https://www.youtube.com/watch?v=1ZZoTUQvwBI

What the video doesn’t show you is how to do it for a K-30 nor how to extract the solenoid. To extract the part on the K-30, there are two tricks missing in the video:
• Unscrewing the solenoid: You should use the bit of a multibit screwdriver to access this. Normally there should be enough clearance and once the glue is removed, you can remove it by hand.
• Taking the solenoid out: You need to bend the top cover case slightly and simultaneously use a pair of tweezers to extract it.

Once it is extracted, you can grind it down. I have shown an example of the ground down part here. Remember to reassemble and test the camera before putting the case back on.

Photo 1: Unscrewing the solenoid. Note the screwdriver bit which comes from a mobile phone screwdriver set. If you search Amazon for this, you should find one. Also, you’ll probably find it handy for opening the camera in the first place.

Photo 2: Extracting the solenoid means you have the carefully bend the top cover by applying force as indicated by the red arrow.

Photo 3: Photo of the actuator in the solenoid once round down. you can see that grinding down the tips are the most important thing to do in order to reduce the magnetic flux going through the horseshoe.