Yashicamat 124G Meter Adjustment

[Born2Late]

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.

 

[cjbecker]

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

 

[ic-racer]

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).

 

[EASmithV]

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

 

[afrank]

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).

 

[henry finley]

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.

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.

 

[C.poulton]

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

 

[afrank]

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.

 

[Born2Late]

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.

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.

 

[afrank]

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.

 

[henry finley]

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.

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.

 

[DWThomas]

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.)

 

[ic-racer]

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.)

Same here.

 

[afrank]

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.

 

[Born2Late]

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.

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.

 

[henry finley]

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.

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?

 

[Born2Late]

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.

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?

 

[henry finley]

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.

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.

 

[Shuichi Suzuki]

Hi BO
I have looking for the forum "How to adjust the light meter of Yashica Mat" , and I saw your post here. My light meter is moving but not accurate, like 4 steps off. I want to use the internal light meter, as you did.
Could you instruct me how you did the adjustment?
Thank you for your help!!
SS

 

[monopix]

For future reference, information is at https://www.photrio.com/forum/threads/yashica-mat-124g-meter-ciruit-design-and-adjustment.153186/

 

[Shuichi Suzuki]

Thank you!! Very informative. I believe the post you shared to me is the only comprehensive and practical instruction for the internal light meter adjustment.
I will try to fix my meter, not break it. ; )
Thanks again.
Shuichi

 

[Mark Lewus]

Thanks!
I bought 5 Yashica Mat 124G cameras on eBay, and as you might expect, not one of them worked properly on delivery. They all needed lubrication of the crank mechanism, which otherwise was extremely stiff. The dials that show the type of film were stuck fast on 4 of the 5 cameras. The front surface mirror and inside of both lenses were filthy on all cameras. Three of the battery holders needed the bottom contact to be reglued. And the meters were all out of calibration by at least one stop, even when using a 1.35V hearing aid battery. Surprisingly, all but one of the shutters were accurate, and the one that wasn’t just needed a minor cleaning. I have them all repaired except for meter calibration, and while I have them apart I’m going to re-calibrate the meters to use 1.55 V silver-oxide cells.

I decided to build a variable light source to more easily calibrate the meters on these and also other cameras that I repair. I used 30 feet of high intensity 12v 5000K LED strip in a box with a 300x400mm clear panel and fresnel lens that I recovered from an old LCD display. I can reliably get EV6 to EV16 from this setup as confirmed with a modern light meter, so I can accurately calibrate the Yashica meters.

The only thing I needed was the calibration information, which is not in the manual and was surprisingly difficult to find online. Thanks so much for providing it.

Mark

 

[ic-racer]

Good work on those repairs!
I had been using an small light box for meter adjustment on vintage cameras, but when I used it with a modern (Nikon F100) camera it would not meter correctly because the 60 Hz flicker of the fluorescent lamps in the light box. Do your LED drivers flicker?

 

[Mark Lewus]

No, I don't see any flicker - anymore. The LEDs are driven by a 12VDC source, through a pulse-width modulated power controller to set the brightness level. Initially I was getting beat frequency flickering. The controller runs at over a 100KHz but any unsynchronized frequency will beat against a fixed frequency source, like the sampling done in your camera's meter. I added a simple undamped LC filter at the output of the controller. A 1mh/10 amp inductor and 2,200uf/25V capacitor gives a cutoff frequency of 107Hz, well below the pwm frequency. That is probably overkill but I had the parts in my parts box I get no noticeable flicker even when viewing a video recording of the panel, which is where it would be very obvious.

If you want to try this, the LEDs that I used are available on Amazon. They are "HitLights cool white 2835 LED light strip 5000k, 1738 lumens per meter, 4.6 watts per foot." They come in 10 foot strips with three LEDs and a resistor on 1 inch centers. I bought three sets and cut them into 22 x 16 inch pieces, powered in parallel. The controller is a "Supernight LED light strip dimmer, 12-24v 30A PWM dimming Controller" also on Amazon. I powered it with a Meanwell 15V 200 watt power supply that came out of my parts bin. I set the power supply for 10 amp draw (~13.3 volts) to provide EV15. 14A draw (~14.9 volts) will provide EV16. The voltage levels are approximate and will vary from lot to lot. So it's best to set the current rather than the voltage. This is because the forward voltage of the LEDs vary and they're driven through a resistor. Thus the current drawn is not at all linear with regard to the voltage applied.

I added six 1 inch vent holes at the bottom and top of the box, which is adequate for occasional use. If you're going to use it continuously you should add a 60mm or 80mm 12v fan to vent the box, as the LEDs dissipate over 100 watts. I also added a 15 amp fuse in the +DC lead to protect the power supply in the event of a short.