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June 2010: Zenit TTL

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Voir texteThe owner of this camera has tried to adjust the lightmeter, but got only outliers. Two adjacent positions of the film speed selector give the same readings, and there is an abnormal difference between the positions corresponding to 1/250s and 1/500s.
This body from 1982 is equipped with flash shoe with sync contact, but it is broken.
The shutter operates properly, film advance and shutter release are smooth, the lens iris closes properly while metering and shooting. The lens mount is loose, three screws need tightening.
The foam wedging the pentaprism needs to be replaced, as usual...

Voir texteHere is how the electrical circuit of a Zenit TTL looks like (taken from another camera). While on many cameras, the film speed selector is made of a variable resistor (graphite track), here it is made of a series of fixed resistors. Same behind the shutter speed selector. This system is very reliable over time, indestructible while a graphite track wears out and may suffer from moisture. Combined with the robustness and simplicity of the body, it gives the all terrain of the camera.

Voir texteControl of the resistors: as supposed, two parallel resistors have the same value!
This body is thus defective since its manufacture! What is even more annoying is that the wrong resistance value corresponds to the position closest to ISO 200, and that there is practically on the present market only ISO 200 film!
Compared to the resistors of my circuit, from a 1978 camera, the values are significantly different, which allows me to assume that the CdS sensor manufacturing has evolved between the two bodies, and the resistance values have been recalculated accordingly. It will then be necessary to exchange the complete circuit to avoid problems.

Voir texteI bought on eBay two Zenit TTL for parts. These are "Olympic" versions, presumably from 1979-1980. I will wait for them to compare also the resistor values.

Meanwhile: replacement of the flash shoe.

Voir texteThe "wrecks" arrived. Circuits are the same version as the original, I took the cleanest one (after controlling resistances!).
To remove the electrical circuit the pentaprism must be removed, which releases the sensor, attached to the plastic optical system for guiding light.

Voir texteHere is the circuit removed. There is a delicate point, when removing the galvanometer, to avoid bending the needle (a notch is provided, it must make 1/4 turn off after unsticking a small cache).

Voir texteAnd the "new" circuit in place, pentaprism foam changed.

Voir texteTo adjust the lightmeter, you must return the cover and buttons. The setting is made through the hole at the top right, usually closed by a screw, by turning the adjustable resistance. This setting is quite tricky, I had to make a film to check the result, and then re-adjust.

Here it is, the Zenit TTL is gone back to it's owner...

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