John:
Of course, there is a limitation in terms of maximum shutter speed, but the idea behind all this discussion is if it´s possible to modify the original electronic design in such a way to admit working with higher ISO ratings.
There is no "program" in those cameras (I´m limited to YE 35 XYZ) just a simple analog circuitry very well designed in terms of economy of components but with some tricky array of sliding switches inside (POD and related elements).
As simple RC circuitry, which charges to "read" the lighting and discharges to control the shutter, it should be possible to modify it, however it won´t be an easy job.
The question if the CdS cell response is linear or log, is very interesting one as the circuit itself doesn´t behave in a linear manner as long as the charging curve of a capacitor though a fixed resistor isn´t also linear. And as far as I see there is no constant current supply in this design...
Perhaps what Yashica engineers did was to use the CdS cell in a range of lighting where it is more or less linear, and select the switching points of the transistor array to lie within those limits. Then, the circuit becomes almost linear within a limited range of light and voltage. Then ... the two resistors one in series and the other one in paralell.
In fact I´m not eager to modify any of my cameras in such a way, unless having enough time to experiment it, and having also several of them (to have spares) as the modifications may lead Us to the resistor array inside the shutter. It would be nice, but I won´t face the risk of turning a fine camera into junk. Any way, you´re right, life is too short...
Meanwhile, where did you get the YE 35 service manuals? may I PM you?
Thanks for a very interesting discussion about one of those "what if...?" that everybody´s live may have.
Regards
Ernesto.
