Sunday, July 19, 2020

Pentax K70 DSLR (K50/K30) - Dark photos fix - Solenoid replacement

Unfortunately, due to a failed cost savings attempt on Pentax' side the solenoid manufacturer Shinmei moving its production from Japan to China, a different (cheaper?) aperture solenoid was used on their K30, K50 and later a slightly? improved version on the K70 model cameras. 
There are basically 2 versions of the now famous culprit solenoid used in the Pentax K series: the most recent has a plastic (PET) body of green color and it is made in China. The former/older solenoid used in their older cameras such as the K10, K20, K100 uses a higher quality white teflon (PTFE) body solenoid that was made in Japan.

This issue is well documented in several posts at the, reddit, etc. 

A few links that are worth reading before you begin working on this fix:

Fixing the Pentax K70:

To fix the K70, a K20 was used as the donor camera. 

IMPORTANT: It is highly recommended to use a body mount cover while performing this "surgery". I didn't use one and was very careful not to drop anything in the sensor/mirror assembly.  

I couldn't find a tutorial on how to open the K20, but I did find the K10 service manual. The K10 model is an older but very similar model to the K20:

Opened K20D - Careful when lifting the top and front parts as they have fragile cables connected to them

K20D - Showing the white solenoid

K70 - Opened, ready to have the green solenoid removed

K70 - With the green solenoid removed

Solenoids side by side: on top/left is the white one with the green on the bottom/right 

K70 with the transplanted white solenoid in place of the original green one

SUCCESS! The K70 started working again after the white solenoid was installed!

As for the K20, I did an attempt (this is non-recommended as a permanent solution) to repair the green solenoid by sanding the 4 corners of the metal plunger:

Sanded green solenoid plunger

God knows for how long it will last (*), but the K20 with the green (sanded) solenoid is also working!

(*) again, sanding is a temporary and not recommended solution as it will most likely fail after some time. Also, sanding can cause the metal to rust and eventually blocking the plunger altogether. I don't use my K20 anymore so, this was an acceptable experiment to me.


Fixing the Pentax K50:

The K50 in question is suffering from the same dark photos problem as the K70.

In order to fix the K50, a donor K100 from 2006 was used. Opening the K100 is similar to the K50, just be organized and mark where every screw comes from - these are the sketches and screw tray I used:

iFixit Screw tray with my hand made screw mappings

Another good reason to use a K100 as a donor camera is that most K100 (it depends if the model is for the NA or EUR market) have 2 white solenoids in it: one for the aperture and another one to control the flash. Removing the flash solenoid is simpler, so that's what I decided to do.

Lifting the upper part of the K100

Lifting the top cover reveals the white flash solenoid that controls the flash opening

As there isn't much space to desolder the 2 wires on the solenoid end, I desoldered the flat cable end

White flash solenoid from the K100 removed

K50 opened with the green solenoid exposed - ready to be swapped

PS: I installed the green solenoid removed from the K50 (sanded as well) into the K100. It is working ok to control the flash opening. 

SUCCESS! No more dark photos on the K50 as well!


  1. You can use the green Chinese solenoid in the flash of the K100D or any Pentax with a solenoid in the flash but I would not use it for aperture in the K20D. Too many uncertainties but you wrote about that. Sanding a solenoid is one of the worst solutions.
    Photogem from

  2. I used to fix copiers. Lots of solenoids. Honestly unless the coil shorts out, the one reason solenoids don't work is either dirt, grease, or poor fit, 9 times out of 10 we could clean the solenoid plunger with alchol or similar cleaner and it would work again. Hope that helps.

    1. The problem with these Pentax solenoids seems to lie on the different materials used. While the green solenoid body is made of PET, the white one is made out of PTFE. PTFE is a better material (stronger and with less friction), while PET will inherently age faster than PTFE for such application.