Repairing an in-camera selinium meter

Discussion in 'Rangefinder Forum' started by Tony-S, Jul 7, 2011.

  1. Tony-S

    Tony-S Member

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    I just picked up a Fujica 35-SE with an f/1.9 Fujinon lens that is in very good shape. The aperture blades were a bit sticky and I cleaned them and the shutter blades with lighter fluid and they are working great now. Other than a few cosmetic blemishes, the only other problem is the light meter isn't working. A search of the 'net suggests that usually the selenium cells in these cameras are just fine; the problem resides with corrosion of contacts. Does anyone have experience with getting the actual problemsidentified and the appropriate fixes for them?
     
  2. bsdunek

    bsdunek Subscriber

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    I have repaired hand held light meters by using a pencil eraser VERY LIGHTLY on the contact surfaces of the selenium cell and it's contact 'fingers'. I do understand that selenium cells deteriorate also. It seems to be time in light that does it. I've read that you should keep your light meter in the dark except when you're using it. Just what I've read, I don't know.
     
  3. BobD

    BobD Member

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  4. Ottrdaemmerung

    Ottrdaemmerung Member

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    Recently the Film Photography Podcast has mentioned a spray called DeoxIT that works well for restoring life back to oxidized or corroded contacts; they used it for working primarily on Polaroid cameras. I wonder if it would help the contacts on selenium cells. BobD's link above would seem to indicate that it would. Amazon sells cans of DeoxIt for about $10 and I've considered buying one.
     
  5. Ralph Javins

    Ralph Javins Member

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    Good morning;

    There are two ways that problems come up with the Selenium cells. That first already mentioned is the contacts. The use of DeOxit or a similar cleaner will work nicely. Just keep it where it is to do its job. The use of a "Q-tip" type cotton swab or even a toothpick to put just what you need on the spot where it is to go is important.

    Normally I do not recommend the use of a pencil erasure or something similar in an attempt to remove any suspected corrosion from electrical contacts, especially those on printed circuit boards (PCB). Most often they will have a very thin gold flash coating only a few molecules thick that serves as an anti-oxidant covering on the contacts. The pencil erasure will easily remove that gold flashing and leave the base copper layer underneath now exposed to the atmosphere where it really begins to develop an obvious green corrosion.

    In most cases, just the use of a cotton swab and alcohol is all that is needed to restore a clean contact surface.

    The second and more serious failure mode with Selenium light cells is a failure of the sealing around the edges of the cell layers allowing moisture in the atmosphere to work in there and degrade the cell over time. There is no real indication that this is accellerated by exposure to light. In this case, the only real cure is to replace the Selenium cell. There are still companies who can make the size Selenium cell to replace one in your camera.

    Here in the United States, Quality Light Metric in Hollywood is probably our best for Selenium cell light meter repair. There is another company in London whose name begins with the letter "M," but I cannot think of it just now. I will probably remember after hitting the "Post Quick Reply" button.
     
  6. Tony-S

    Tony-S Member

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    Thanks everyone; excellent info. I will probably post photos of the surgery if I have problems. Hopefully it's just a matter of cleaning the contacts well.
     
  7. Leigh B

    Leigh B Member

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    DeOxit is an excellent product designed for a very specific purpose...
    It reduces silver oxide back to metallic silver, and does it very well.

    It's not a general-purpose contact cleaner, as some folks would have you believe. And it's quite expensive as compared with standard contact cleaners.

    But as I said, it works very well for its intended purpose. I have both the spray and liquid versions in my repair stock.

    For general contact cleaning, particularly of gold-plated contacts, a pencil eraser applied very gently works wonders. Regarding Ralph's comment above, the eraser is not intended to remove corrosion, only surface contamination and dirt. And it's quite cheap.

    - Leigh
     
  8. edp

    edp Member

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    Yes, it's moisture not exposure to light that kills selenium cells.

    Sadly, Megatron are no longer trading. They did a good job on my Weston Master V lightmeter.
     
  9. BrianL

    BrianL Member

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    Deoxit comes in several versions so make sure you get the right formula for contacts and not another such as for sliders. It is common in many places selling electronic supples and is heavily used by vintage audio nuts so if you know someone who knows someone in the hobby maybe he'll lend you the can. Make sure if you get a contact cleaner it is safe for plastics as many formulas are not.
     
  10. Leigh B

    Leigh B Member

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    Good advice, Brian. :D

    I work on vintage radios and amateur equipment, and find DeOxit quite useful.

    Good point about plastic-save cleaners.

    - Leigh