This applies to all Zenits with a Selenium cell or TTL metering with a screw here
(see photo). It is not allways nessecary to take your camera apart to replace the seleniumcell. On some models it is very easy to adjust the meter, these models are the Zenit EM, 11, TTL (with an exception of some early models) and the 12. The Zenit ET and the Zenit 10 consists of several types both with and without a lightmeter. Some of these can be recalibrated.
If you remove the screw you will faintly see another small screw beneath. With this you can calibrate your lightmeter. Just take out a good working lightmeter or another E-type or any other camera, with a readable lightmeter that is.
Adjustment really is that simple. And it saves you the task of dismanteling your camera. Unfortunatly if the selenium cell is dead you will have to. Or you are stuck with a handheld meter. This only works if the cell is of by 1 or 2 stops. If it is 3 to 4 stops it might not be possible to adjust the meter at all.
A word on TTL metering and batteriesAs all my repair articles go this is done at your own risk.
Some of the Zenit TTL cameras use 1.35 volt batteries, as these become in short supply and hard to get it is possible to use 1.5 volts. Unfortunatly since the metering system is calibrated at 1.35 volts it is possible that the meter will now be off by 1/2 or even 1 stop.
The main problem is that the 1.35 volt batteries were mercury based. This ment a steady 1.35 volts flow. Then after several months the voltage went down very fast. Which automaticly ment that the meter became erratic or just stopped.
Present 1.5 volt batteries (usually alkaline) run down differently. So after af few months of use it will be 1.4, 1.3 ect. Which could result in a lightmeter that suddenly can go up or go down a notch. But not allways. A major problem would be if the Zenit 12XP or any other TTL Zenit used the 1.35 volts as a reference for the meter. In that case the meter would be off by a stop (more or less).
So I decided to test it out.
I took my Zenit 12XP (aka SD) and put in fresh 1.5 volt cells. Measurement OK.
So re-testing with 1.5 volts which are down to 1.3 volts. Measurement OK.
The electronics in the 12XP are more advanced than I thought. So it was time to open up my 12XP's. A all black full metal one from 1986 and a half metal half plastic one from 1989. The electronics are identical.
And it also means that the electronics do not use 1.35 as a reference. So it means KMZ put some kind of circuitry in there that deals with the 0.15 volts difference. Unfortunatly not all the components can be read. Which means I would have to measure up the entire circuit just to find out how it is made. At this moment I don't really feel like doing that. The TTL and the Early 12 are different, they were built for 1.35 volts. The later 12 series, easily recognized for it uses 2 batteries instead of 1 big VX cell, handles only 1.5 volt cells, but also works with 1.35 volts cells.
So here is a small overview of batteries and commonly used Zenits,
On the subject of batteries, I highly recommend this article both in English and in Dutch. Which is perfect for the engineers among you. It is an great piece of research and work.
Mercury battery problem and various solutions
Het kwik batterij probleem en de diverse oplossingen