Jumpy light meter on 124G

bvy · May 9, 2015

I have a Yashica Mat 124G with a faulty light meter. It wants to work, but most times it's dead. I've opened the top in hopes of finding something loose or disconnected, but no luck. It has a fresh battery and the tiny circuit board behind the light acceptor window receives a consistent charge from the battery. So it's not the switch or anything between the battery and light meter assembly. A little bit of probing or a slight localized impact (knocking etc.) seems to activate it. It might respond for a short while, or indefinitely if you don't touch it. Usually it jumps around.

Any ideas what else I could try? I've probed, jiggled, and held things in place to see if I could find the bad link, but I can't pinpoint the problem any better than this.

PS: PLEASE no responses to the effect of "the light meter is useless anyway." I have my reasons -- my question is about what's wrong and how I can fix it. Thanks.

tkamiya · May 9, 2015

My bet is on the switch. As you know, when you open the viewing hood, it activates the light meter. The current flowing through it is so low, it is insufficient to break through the oxidation of the mating contact. If you have spray deoxidizer (sold under various names), you may try it but don't spray. Spray into a small container and use a Q tip of even a tooth pick to apply to the contacting surface. OR, you can use something like a copier paper or a business card paper to varnish the surface. DO NOT use sand paper....

bvy · May 9, 2015

Well, like I said (or maybe I didn't), I used a voltmeter to check the current on the tiny circuit board just behind the light-receiving window. The current is consistent even when the meter is not responding or jumping around. So I don't think it's the switch...

shutterfinger · May 9, 2015

I used a voltmeter to check the current on the tiny circuit board just behind the light-receiving window. The current is consistent even when the meter is not responding or jumping around.

Did you place the meter leads between one of the battery terminals and the battery socket to read the current? Are you sure the current is correct for the meter when reading correctly?
Place the negative meter lead on the negative battery terminal and measure the voltage at each side if the switch with the switch in the closed position, any difference is wear or corrosion in the switch.
Very dull gray solder joints may be breaking down or crystallized solder joints are bad. Some circuit board solder joints crack around the component lead and high magnification is needed to see it.
Another possibility is a component is internally failing.

tkamiya · May 9, 2015

If you had a voltmeter connected, you had the top off. So the switch was on "connect" position. In actual use, this switch is actuated every time you open and close the top. These intermittent issues are hard to track. I usually start from "most likely to be the problem" area and move onto lesser and lesser possible areas.

On any circuit, switches and potentiometers (with moving parts) are most likely problems. So I'd still start there. If in doubt, bypass the switch and directly connect the power, just to be sure.

I've been doing electronics repair for many years (professionally in past and at hobby level today). That's how I would approach it. I don't guess. Go from most to least. Check and verify every step.

Corrosion and break in solder joints are also possible (as mentioned above). It is not uncommon to reheat every joint with a touch of fresh solder to "freshen up" the connection, too. Sometimes, corrosion forms between leads from components and solder. These are very hard to detect visually. So I would just re-melt the solder like this.

bvy · May 9, 2015

Thanks. This gives me a few more things to try...

I should have mentioned that the light meter worked fine and was accurate before I dropped the camera last fall. Overall damage was minimal, but the light meter was knocked out and into its current state.

shutterfinger · May 9, 2015

I should have mentioned that the light meter worked fine and was accurate before I dropped the camera last fall

Check the circuit and sensor boards for hair line crack(s). High magnification and or back lighting required.

I was a professional electronics technician for several years.

paul ron · May 9, 2015

Droped? Maybe the hair like wires that float on the meter movement are lose?

As mentioned above by others, the switch is generally where most problems come from aside the old lead solder joints. Sometimes refreshing old solder cures the intermittent problems.

Another common problem is the connection to the photocell... It is fragile n old.

.

bvy · May 10, 2015

Okay, I need to get in there with a light and a loupe and check for cracks as suggested. I see nothing with the naked eye. However, the light meter print is loose. Should it be and does it matter? The wires are connected securely, but it's not mounted to anything and moves around freely in the housing. Probing it, however, has no real effect on the meter -- i.e. holding in a certain position doesn't cause the meter to work. I'm referring to the tiny printed board in the link below (not my picture -- just for reference):
https://www.flickr.com/photos/29504544@N08/5004696023

shutterfinger · May 10, 2015

It should be secured to the chassis some way with an insulator between it and any metal part. Loose leaves it prone to other vibration from handling caused failures. A careful inspection may reveal how it was mounted.

David Lyga · May 12, 2015

My first camera, REAL camera, was back in 1966 when I was 16. It was a Minolta Autocord CDS. After about two years the meter needle started jumping. This is largely caused by too much exposure to bright light, like sunlight. This is the primary reason why the CDS meter is now extinct. Back then, as with your Yashica, bvy, this was a major concern but, of course, I did not know that back in 1966. - David Lyga

Brett Rogers · May 13, 2015

Maybe the needle pivot has fallen off its jewels. This will jam it and when it is vibrated a little the pivots will jump around and it will respond a little until it jams again. Fits with your comment that it worked until you dropped it. And won't necessarily manifest as a continuity fault, if the spring isn't damaged. I don't much care for the Yashica twin lenses and will not work on them personally so I'm afraid that's all I can suggest, sorry.

F5B&W · May 13, 2015

bvy said:
I have a Yashica Mat 124G with a faulty light meter. It wants to work, but most times it's dead. I've opened the top in hopes of finding something loose or disconnected, but no luck. It has a fresh battery and the tiny circuit board behind the light acceptor window receives a consistent charge from the battery. So it's not the switch or anything between the battery and light meter assembly. A little bit of probing or a slight localized impact (knocking etc.) seems to activate it. It might respond for a short while, or indefinitely if you don't touch it. Usually it jumps around.

Any ideas what else I could try? I've probed, jiggled, and held things in place to see if I could find the bad link, but I can't pinpoint the problem any better than this.

PS: PLEASE no responses to the effect of "the light meter is useless anyway." I have my reasons -- my question is about what's wrong and how I can fix it. Thanks.

You've already answered the question in terms of functionality. Your best option is to use a hand held meter. Are you trying to repair it in order to sell it?

bvy · May 13, 2015

Brett Rogers said:
Maybe the needle pivot has fallen off its jewels. This will jam it and when it is vibrated a little the pivots will jump around and it will respond a little until it jams again. Fits with your comment that it worked until you dropped it. And won't necessarily manifest as a continuity fault, if the spring isn't damaged. I don't much care for the Yashica twin lenses and will not work on them personally so I'm afraid that's all I can suggest, sorry.

That's the most convincing conjecture I've heard yet -- based on what I'm seeing. I believe all of that's in the small cylindrical housing in the picture I linked to earlier. Sounds like a delicate procedure; I might just call it a loss...

F5B&W said:
You've already answered the question in terms of functionality. Your best option is to use a hand held meter. Are you trying to repair it in order to sell it?

I haven't decided. The camera still works well, but if I decide to sell it, I could regain more of my investment if the meter works. For my own purposes, I have no intention of carrying any more luggage around (i.e. a light meter). The camera's bulky enough and heavy enough as it is -- totally unsuited to the street photography/street portraiture that I like to do. That it takes such damn nice pictures is the only thing that keeps me lugging it around...

Brett Rogers · May 13, 2015

If the meter assembly is not too hard to reach I would try opening it up and if I am correct, gently re-installing the needle assembly onto the jewels and if necessary, re-adjusting it until it is secured in place with a little running clearance. You might even have to back off the adjuster just a bit to re-install it first, it may make it easier, anyway. A meter that hardly ever works at all is very little better than one that is completely stuffed, so it is not like you have a great deal to lose by having a crack at it.

Andrew K · May 14, 2015

some cameras from that era had small rubber stops that the meter needle would rest on when switched off/was "over range" (left or right side) - these become sticky over time. I can't recall if this is one of those cameras, but if it is the solution is to remove the rubber stoppers and replace them with small synthetic stoppers.

Brett Rogers · May 14, 2015

Andrew K said:
some cameras from that era had small rubber stops that the meter needle would rest on when switched off/was "over range" (left or right side) - these become sticky over time. I can't recall if this is one of those cameras, but if it is the solution is to remove the rubber stoppers and replace them with small synthetic stoppers.

The Minolta SRT101s and their ilk are a case in point. If the meter of one doesn't move, and the battery chamber/wiring isn't crusty, there's a pretty good chance the meter needle is glued to the foam bumper.

F5B&W · May 14, 2015

bvy said:
That's the most convincing conjecture I've heard yet -- based on what I'm seeing. I believe all of that's in the small cylindrical housing in the picture I linked to earlier. Sounds like a delicate procedure; I might just call it a loss...

I haven't decided. The camera still works well, but if I decide to sell it, I could regain more of my investment if the meter works. For my own purposes, I have no intention of carrying any more luggage around (i.e. a light meter). The camera's bulky enough and heavy enough as it is -- totally unsuited to the street photography/street portraiture that I like to do. That it takes such damn nice pictures is the only thing that keeps me lugging it around...

A Sekonic L-208 is about the size of a wad of house keys and can easily slip into a jeans pocket. It does the same thing as the camera meter, maybe a little better.

The nice thing about a waist level TLR is that it isn't as obtrusive as pointing an SLR at someone's face. The shutter is whisper quiet also, not having to flop that big mirror over. I'd say you have a damn good tool for street photography.

Ko.Fe. · May 15, 2015

You could do both, fast street photography and slow street portraits with TLR.
124G is small enough, fast to advance and cock the shutter.
I used Yashica A II, Lybitel 2, Mamiya C33 and Rolleicord III as well for street, candid and posed portraiture.
Works like a charm. Vivian Mayer had the same opinion, I think...

Jumpy light meter on 124G

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