I was looking for this information, but did not find it on the web, so I thought I'd post it here for future reference.
Here is the circuit for the CDS meter on the Yashica Mat 124G.
The 2 potentiometers (Pots) are labeled for laterality as seen on the photo below. The CDS is a tandem device with an electrode in the middle - I could not find a modern replacement as most cells are single devices, but fortunately they do not often fail. The Right potentiometer should be adjusted in bright light, and the Lt potentiometer in dim light. Under bright light, the CDS has low resistance and over rides the Left Pot. Under dim light when the CDS has high resistance, the Left Pot can now trim 1/2 of the CDS. The calibration process is to go back and forth between bright and dim light, and adjust the respective Pots until the meter reads correctly in the range of interest.
The meter circuit and mechanics can be exposed by removing the waist level finder (4 screws) and the back plate on the meter head (2 screws). As you can see, there are a number of mechanical adjustments available as well. The cylinder in the middle is the meter movement, it is on a gimbal such that the ISO changes(top right) and the shutter speed changes couple by the arm on the bottom right, can rotate it. Aperture changes are independently communicated by the arm on the lower left to the yellow follower at the top. Notice that the Shutter and Aperture coupling arms have large notches in them these are for course adjustments, done by widening the notch. The eccentric screw at the bottom right allows you to change the pivot of the shutter coupling arm, effectively shifting the range of the meter.
If the electrical adjustments cannot get your meter into the calibration range, then a mechanical adjustment can be made to the meter mechanism to shift the range, either coarsely by bending the coupling arms, or finely by the eccentric screw.
In this case, you'll notice the Right Pot is at it's max limit, so an adjustment of the eccentric was necessary to bring the meter into range. The current meter is now withe 1/2 stop of my reference, and has been recalibrated to us a 1.55V Silver Oxide battery.
If permissible, I can cross post this in the Repairs & Modification forum. I placed it here because I do not often visit that forum.
Here is the circuit for the CDS meter on the Yashica Mat 124G.
The 2 potentiometers (Pots) are labeled for laterality as seen on the photo below. The CDS is a tandem device with an electrode in the middle - I could not find a modern replacement as most cells are single devices, but fortunately they do not often fail. The Right potentiometer should be adjusted in bright light, and the Lt potentiometer in dim light. Under bright light, the CDS has low resistance and over rides the Left Pot. Under dim light when the CDS has high resistance, the Left Pot can now trim 1/2 of the CDS. The calibration process is to go back and forth between bright and dim light, and adjust the respective Pots until the meter reads correctly in the range of interest.
The meter circuit and mechanics can be exposed by removing the waist level finder (4 screws) and the back plate on the meter head (2 screws). As you can see, there are a number of mechanical adjustments available as well. The cylinder in the middle is the meter movement, it is on a gimbal such that the ISO changes(top right) and the shutter speed changes couple by the arm on the bottom right, can rotate it. Aperture changes are independently communicated by the arm on the lower left to the yellow follower at the top. Notice that the Shutter and Aperture coupling arms have large notches in them these are for course adjustments, done by widening the notch. The eccentric screw at the bottom right allows you to change the pivot of the shutter coupling arm, effectively shifting the range of the meter.
If the electrical adjustments cannot get your meter into the calibration range, then a mechanical adjustment can be made to the meter mechanism to shift the range, either coarsely by bending the coupling arms, or finely by the eccentric screw.
In this case, you'll notice the Right Pot is at it's max limit, so an adjustment of the eccentric was necessary to bring the meter into range. The current meter is now withe 1/2 stop of my reference, and has been recalibrated to us a 1.55V Silver Oxide battery.
If permissible, I can cross post this in the Repairs & Modification forum. I placed it here because I do not often visit that forum.
