Yashicamat 124G Meter Adjustment

Discussion in 'Camera Building, Repairs & Modification' started by Born2Late, Feb 5, 2013.

  1. Born2Late

    Born2Late Subscriber

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    Can anyone advise me about the functions of the 2 potentiometers on the Yashicamat 124G light meter? I suspect one is gain and the other offset, but I could be way off base.

    Mine reads too dark by about 4 stops. It appears that the switch works properly and I am using a hearing aid battery with adapter.

    Yes I have a good hand held meter, but would like to get the built in meter working at least in the ball park.

    Any help with adjustment would be appreciated.
     
  2. cjbecker

    cjbecker Member

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    No but all I can say is the best light meter is your eyes and brain. Just go by your gut.


    All depending if you shoot chrome's though
     
  3. ic-racer

    ic-racer Member

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    Yes, the Yashica 124g service manual I have only is an assembly manual with no mention of meter calibration. Maybe the meter is covered in the 124 (non-G) service manual (which I have never seen).
     
  4. EASmithV

    EASmithV Member

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    what if you just adjust the ISO to match the correct setting?
     
  5. afrank

    afrank Member

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    I did calibration on mine once, I decided to ditch the 1.35v baterries and went with 1.5v + recalibration.
    1 of the potentiometers seems to handle the minimum threshold for light sensitivity and the second one lets you fine-tune it. Cant remember which is which but can be easily figured out.
    Just choose a battery type, then meter an opaque wall(brick)? at, f3.5;1/30 -> and then going up +1stop changing fstop
    and then again from f3.5;1/30 -> f3.5;1/500. (always corroborating with a trust-able avg meter.
    My Yashica meters precisely like my spot meter, dslrs and slrs under normal circumstances (no backlight sun/snow/sand).
     
  6. henry finley

    henry finley Member

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    I am NOT, nor ever have been; a certified camera repairman. What I DON'T know about camera repair would fill a volume set of encyclopedias. Havig said that, if you have a meter out of adjustment, then almost certainly you have a CdS cell that has gone out-of-linearity. Translated: bad. I've found 2 stops is too far out-of-linearity to recalibrate. Be sure any sort of solder/corrosion/contact failures are taken care of first. Move on to the variable resistance linkage, seeing to dirty wipers of any kind there. THEN you can move on with attempting calibration with the pots provided. You will then learn the sad truth--your CdS cell has gone weak. If you attempt to re-calculate and replace the fixed resistors in the circuit with ohm's law, you're wasting your time. No calibration will end up linear. Not from 4 stops.
     
  7. C.poulton

    C.poulton Member

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    My 124G meter is about 2 stops out - not sure if its faulty, just the way the meter works (tends to expose more for the sky) or me, however I tend to use a hand held meter in most cases.

    As an aside I have a Pentax Spotmatic who's meter is 2 stops out - I've tried on numerous occasions to fix this, recalibration and even replacement of the meter cells, but to no avail - I just use an external meter now.....


    Christian
     
  8. afrank

    afrank Member

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    If there is light from the sky try point to the ground in a small angle or cover the top and give it shade with the palm of your hand to avoid the sun from throwing it out.
     
  9. Born2Late

    Born2Late Subscriber

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    Results of Adjustment

    I am pleased to report that I have successfully recalibrated my light meter. It does appear that the potentiometer on the right is a gain adjustment and the left one is offset.

    After about 2 hours of work, my built in meter is spot on with my Gossen Luna Pro F throughout the full range of illumination. My Luna Pro was just calibrated by Quality Light-Metric in Hollywood. I highly recommend them.

    So it can be done.

     
  10. afrank

    afrank Member

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    GRATZ! I hate when people treat things/procedures/etc like alien given gifts that are not meant to be tinkered with. Its incredible what a bit of science can do to.
     
  11. henry finley

    henry finley Member

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    Hot dang, aren't I standing here with mud on my face. It's fine with me, though. Glad you got it done. I have only 2 questions: Were you sure you were 4 stops off? that's a lot. and 2) what kind of linearity do you have now? That is, is it calibrated at one light level, or is it showing accurate from dark to bright (linear)? Anyway, good show. I thought it was useless.
     
  12. DWThomas

    DWThomas Subscriber

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    Thanks!

    I have filed these comments for when I some day get around to opening up my 124G. (So far I've been using a separate meter.)
     
  13. ic-racer

    ic-racer Member

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    Same here.
     
  14. afrank

    afrank Member

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    I have an unedited video about dismantling and reassembling the mat 124g, maybe I will upload it one day when I get around editing it.
     
  15. Born2Late

    Born2Late Subscriber

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    I only checked once, but it took 4 full stops before.

    After adjustment it was within 1/3, maybe 1/2 from full sunlight to average interior room lighting. The built in meter is hard to read real precisely. That was reading an 18% gray card.

     
  16. henry finley

    henry finley Member

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    Well, it doesn't get any better than that. I'm glad I was wrong. Just because I'm a good technician, it's tiresome being a know-it-all. Got no problem with being wrong, as long as I'm learning. Learning is all the fun. Knowing everything is boring. Good for you friend--another good repair. Ain't it a thrill?
     
  17. Born2Late

    Born2Late Subscriber

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    Now I have a new calibration project.

    I just picked up 2 Minolta SRT 201's and one meters about 1 stop off.

    Got to figure out where to start.



     
  18. henry finley

    henry finley Member

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    I did a 101 about a year ago, but I can't remember what all I did. I wonder if I have a service manual on CD somewhere. All I remember is some knucklehead before me had strung the meter linkage all wrong. I finally got thing sweet and fine. You'll get it. If I can, you certainly can.