You may have tried to use your
exposure meter on your Kiev 4a and found the situation to be pretty
hopeless. Maybe you are one of the lucky ones that has a meter that
is pretty good. If so then skip this, otherwise for the rest of you
there is a rebuild solution at hand. Let's break it down for you...
Remove this screw here but watch out!
There's a little ball that you don't want to loose. It may pop out
on its own. It's a bugger to find when it is on the floor.
Don't loose this stupid little spring either. Also hard to find when
it bounces away on the floor.
We're going to peel the layers back like an onion. I can assure you
there will be no tears. Pull the inner most ring off and keep going
until I say stop
Note the position of the riveted stops on this next part. You could
put it back in rotated 180 and things just won't be right.
Wavy washer under this one.
Lift the Exposure Compensator dial to reveal part of the
business, the Carbon Resistor element.
Flip over the Exposure Compensator dial you'll see the wiper that
contacts the Carbon Resistor Element.
Chances are the wiper on the Exposure Compensator has worn a groove
down to the substrate over the years. This is one key area where
things can go wrong as the wiper is not making good contact with
resistance material any more. What one can do is bend the wiper so
that it contacts a fresh part of the Carbon Resistance Element. To
go further you'll need to remove the top casting.
If you want to remove the Carbon Resistance Element then flip over
the top casting to remove these three screws.
Remove the base part that the exposure assembly mounts to.
Undo the screw that connects the wires and the Carbon Resistance
Element if free to exchange with another one or for what ever
purposes. You'll see that this one is pretty worn out.
There are some potential solutions to rebuild this carbon resistor
but first some observations. I've taken
some resistance measurements from a Carbon Resistance Element that
was not too worn. At each f-stop setting a resistance
measurement was made with the resultant plotted curves for two
example shutter speeds. You'll see that the curve for 1/500 shutter speed when
compared to an Exponential Curve, things match pretty good until
after f2 then at f1.5 it departs from the exponential curve and this
maybe due to error or the trend doesn't behave at these values.
The trend in the most usable f-stop range indicates that the Carbon
Resistance Element is not linear but exponential. Interesting...
Here's the readings for the actual Carbon Resistance Element that
was removed in the above images for 4 different shutter speeds. It
looks pretty messed up if you ask me.
After changing the Carbon Resistance Element with a better one and
bending the Exposure Compensator Wiper so that it contacts a fresh
area of carbon I get the following curves for 1/50 to 1/500 shutter
speeds. Looks much better, possibly usable but still not perfect.
Discussion to consider: It may be possible to use the
resistance element from a potentiometer used for audio applications
as those have exponential curves. I've not taken the concept further
other than a brief look and found some rotary audio potentiometers
that may house some potentially useful parts as replacements.
Next to get at the Selenium Cell. This is the other part that can
fail due to age. They break down with exposure to moisture and age.
Fortunately new Selenium Cells can be acquired fairly easily that
are used in the FED 5b camera.
First the tricky part, the bezel for the exposure adjustment needs
to be removed. You can make a fancy little tool by grinding used
Exacto knife blades with a Dremel rotary tool, or you can use a very
small set of piers but you'll probably make a mess and scratch
Remove these four screws.
Remove the top stamped metal housing.
Remove the two screws that hold the front meter panel.
You don't need to but you can remove the whole top stamped metal
part at this time.
Four screws hold the shoe mount in place. Make note of that little
springy thingy left behind.
Remove the one screw left at the right side to remove the top
casting to get inside revealing the meter movement and such.
Here's where fun starts. The front sensor diffuser with the selenium
cell slides up as indicated.
Here's showing it from the other side. There is a flat friction
spring that makes contact with the back substrate of the selenium
Keep sliding the selenium cell out while pulling the wire back.
Here's the selenium cell in all it's glory. Unsolder the green wire
to remove the cell completely.
This is the new FED 5b selenium cell inserted into the diffuser. You
will note the new cell is smaller than the stock one. To work around
this I've applied some shim material to make a nice friction fit
centered in the diffuser. You can use any thing for shim material,
toothpicks, coffee stir sticks, what ever you have on hand.
Ready to be inserted back into the housing. See the flat spring that
contacts the back of the selenium cell. Make sure what ever you use
for shim material does not interfere with the flat spring making
Solder wires together.
Put the friction spring back into the shoe as such. Finish assembly
and ready for calibrating.
Comparing the new selenium cell with an old stock one we find there
is a slight difference in values. The old cell has a larger area
which probably explains the difference.
You can adjust out any resistance differences by loosening these two
screws and moving the position of the wiper until you get similar
values. I don't have good data to suggest what these should be but
the above graph my help get you in the range.
Remember this part? The screw also is for adjustment of the meter
movement where you can fine tune your system.
September 07, 2008