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Cleaning and Repairs
Exposure Meter

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

 

Some washers...

 

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 things up.

 

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 cell.

 

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 good contact.

 

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