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 Pentaxforums.com, reddit, etc.
A few links that are worth reading before you begin working on this fix:
Also, a very useful hint prior to start using a regular philips screw driver to open these devices:
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!