Pots … no, not that kinda Pot.

So, got the mechanical parts working on the Yashica Mat-124G … now to figure out how to adjust the light meter.

This camera has a CdS light meter which requires a battery, unlike the burnt out selenium light meters that many older cameras started out with. Sometimes these meters is just not right anymore and require adjustment … sometimes they just don’t do nothing.

A basic circuit consists of a CdS photoresistor, a resistor/potentiometer, power source, and a galvanometer … so how hard could it be to adjust … the Yashica Mat-124G appears to have two potentiometers … hmm.

The first thing to do is to remove the hood. On the left side of the body is a lever that turns the light meter circuit on and off as the hood is opened/closed. The big round thing in the back of the light meter is the galvanometer. To the left of it are the two potentiometers. There are two arms that are coupled to the shutter speed and aperture dial. The speed arm rotates the galvanometer, while the aperture arm moves the aperture target (the yellow arm).

One thing that I did find was that the galvanometer has a cap that the aperture target is attached to. The target arm is pushed as the aperture dial is moved. The seal that was holding the cap in place was broken, so the cap was not in its correct position (looks likes one of the previous owners had dislodged this and also bend the galvanometer arm) … I figured out that the aperture should be set wide open before repositioning the cap.

Trial and error … playing around with all the parts I got the meter to read almost accurately. I still have to figure out the best position of the potentiometers to get some accuracy in low and bright lighting conditions.

… and I say again, thanks to Rick Oleson’s handy dandy CD of tips and for sharing his vast amount of knowledge -> http://rick_oleson.tripod.com … and also Hans Kerensky -> https://www.flickr.com/photos/29504544@N08/albums

 

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