Before you start, please get through this guide at least once. You are following this guide at you own risk. I am not responsible if you destroy your camera!
2.1 Top Cover removal
I started with removing the wind lever. Remove the top which is just screwed on to the lever. Move the plate clockwise and counter clockwise.
Now we need to remove the two plate. The upper one needs to spread apart in order to remove it.
Finally remove this screw with a spanner.
Removing the wind lever is done and we start removing the ISO/Exposure compensation dial. In general it has similarities to the Time/ISO-dial of regular L-Prakticas.
Move the plate slightly clockwise and counter clockwise. Usually it just pops off since the glue is more 40years old and dry. If it is stick, try it with isopropyl alcohol.
Remove the screw and remove the plates
remove the last two screws.
We are done with the dial. Now we start removing the rewind lever and the shutter speed dial.
Lock this "fork" and turn the lever counterclockwise.
Take your spanner and unscrew this locking ring.
lift the parts.
Unscrew this screw to remove the viefinder shutter. Also unscrew the two other screws...
...and two more on the front side.
There are two more screw at the hot shoe. Remove the covering plate by lifting it.
Unscrew the marked screws. Do not unscrew the other one.
Now you should be able to remove the top cover.
2.2. Front cover removal
Remove the time trigger
Remove the leatherette on both sides of the camera.
Remove the two screws on each side.
Lift up the plastic ring which holds the contacts. Then lift the silverrish ring. After this you can remove the front cover. It is actually one piece of plastic.
2.2. Electronics and Shutter
Remove the black tape on the left, and remove the "plugs"
Continue with unscrewing the four screws.
Now you can take the body carefully apart. Note on the following picture: The battery compartment was destroyed by bad soldering of the previous owner. I connected a temporary battery holder to supply some power for testing. So don't mind that:)
....to be continued..:)
Nowadays it is hard to get a PX21 in Europe for a reasonable price. Sometime they cost 20€ each. As Alternative you can choose a 14500 battery. They have around 3.6V and are available either as rechargable (~7€) or single use (~5€).