Every E type will get this problem sooner or later. The Selenium cell has only got a lifespan of 10 to 15 years. Please do not mail me to tell me that yours has lasted 20 years. I have a Revueflex E (which is a Zenit E) that has a cell that is still working after 32 years. Why? Because it wasn't used much.
At this time I have found the panasonic BP - 2911 C4. It came from an old discarded calculator. Now you don't have to use the panasonic. In fact ANY solar cell will do. BUT the cell you use has to respond quickly to light. This is easily measured.
This panasonic cell is not as long as the original cell but it fits the height. Remember that for every type of solarcell (there are a lot of different types out there) you will have to use another resistorvalue. You'll have to measure how much volts it gives off first. So the best thing to dowhen you are replacing the selenium cell with a solar cell is to remove the old resistor and put in a variable resistor instead. This will give you the chance to adjust and calibrate the lightmeter. DO NOT touch the meter itself. It is delicate and should be left alone. Besides that it is not easily replaced if you brake it.
Once the Zenit-E has been dissassembled you should see this, on ghe right the meter is clearly seen.
Remove the cell by pulling the metal strip outwards.
Now the frontcover can be removed aswel as the Selenium cell.
The old cell is soldered loose and replaced by the new one.
You can fit a 100 Kilo-ohm resistor or a variable transistor. I chose the variable resistor to make adjustments. Here a 100 Kilo-ohm potmeter is fitted for tests and adjustments.
I tested it with a two lightmeters and another Zenit-E (printed Revueflex E) which is fully functional. I tested it under several lightconditions and it gives the right reading. For testing all meters (Revuemeter, capitolmeter and Zenit-E's) were set to 100 iso. The E was then calibrated to this. This is how I found the value of 100 Kilo-ohms.
This Zenit-E from 1972 is now fully functional again.