My contrast dials are possessed?

Discussion in 'Darkroom Equipment' started by angrykitty, Dec 16, 2010.

  1. angrykitty

    angrykitty Member

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    So I'm using an omega c760 dichro head that I attached to a c700 stand with the proper adapter piece. I think the contrast dials are possessed? They keep changing themselves randomly.

    At first I thought it was because I was moving things around while I focused, but then I realized that sometimes I make sure it's perfect, press the go button, and after the print is done the dials have moved themselves around without me ever even touching the contraption. They don't feel too loose, but maybe I'm just used to them?

    Each color does it randomly, but they always go up. To be fair there is a ghost that does actually hang around my darkroom...

    is this a common problem? How might I fix it for cheap/free?
     
  2. AgX

    AgX Member

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    Possesed??
    Well Sean, the owner of this forum, has got another forum that handles such issues...
     
  3. George Nova Scotia

    George Nova Scotia Subscriber

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    I had a look at one of the C760 heads I have. It seems that the knobs are just press fitted it place, friction holding them in place. Since the filters are spring loaded to pull down and if the knobs are loose the filters would pull down, increasing the filtration. It may be possible to tighten up the white plastic dials on the inside by pressing them forward, that's my best guess as to how it's put together. The outside knobs just pull off - maybe a piece of foam placed around the shaft could be used as a friction washer. Or do what I did - pick up another enlarger just for the spare head.

    George
     
  4. Worker 11811

    Worker 11811 Member

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    How about a wave washer sandwiched between two doughnut-shaped pieces of Tyvek?

    The wave washer would supply the tension to hold the knobs in place and the Tyvek would provide just enough slip so the friction doesn't cause undue wear.
     
  5. hpulley

    hpulley Member

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    Some days I complain about the inconvenience of the filter drawer on my old Durst M-300 but at least it can't be possessed like that LOL
     
  6. dehk

    dehk Member

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    I swear my enlarger was possessed before, but figured out I over lubed it later.
     
  7. Worker 11811

    Worker 11811 Member

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    I over tightened the balance spring on mine. Every time I loosened the carriage lock it would slowly start to rise.
    It was funny at first but I finally had to take it all apart and fix it.
     
  8. Mark Crabtree

    Mark Crabtree Member

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    Don't bet on it. Well, maybe not the filter drawer, but the filters.

    I need to remember who borrowed my step tablet so that I can figure out which of my Multigrade filters need exorcism (via the trash can). Last night I got inexplicable (or at least unexpected) large contrast jumps between #3 and 3.5.
     
  9. hpulley

    hpulley Member

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    Yeah, some of my old MG filters have degraded, that is true. I'm probably overdue for a new set except that I am looking at getting an enlarger for 6x7 now and it will likely have a color head.
     
  10. angrykitty

    angrykitty Member

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    hmmm im gonna give the wave washers a shot and see if that works... if not ill try that thing from the inside with the plastic... and if that doesn't work ima callin in the priest lol! Thanx!
     
  11. Ian C

    Ian C Member

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    Here is the denouement to Angry Kitty’s perplexing filter setting problem with her Omega C760 Dichroic Lamp House that behaved as if it were haunted.

    I sent her the following on December 27, 2010 after examining a C760 dichro head:

    “The top cover comes off easily by removing the single knob screw at the rear of the top panel. Lift the rear edge of the top panel to remove it. That exposes the Styrofoam mixing chamber and the filter mechanism. This is exactly what you’d do as a first step in gaining access to the bulb to change it. The Chromega C760 is a much easier to disassemble to this point than the Chromega B head, as no small screws are involved.

    As you turn the filter knobs you can see how the rotary cams lift the individual filter panels upward against their hold-down springs. You may need a flashlight at this point to illuminate the mechanism so that you can see it.

    This is almost identical to the Chromega B mechanism, except that the C760 has white plastic or nylon cams instead of the Chromega B’s aluminum cams. The other difference is the white-light cam plate parallel to and just inside of the front panel. The Chromega B has no such feature.

    If you examine the action of the cams as you rotate the operating knobs, I think that you’ll see that the return springs couldn’t possibly make the filter knobs rotate.

    Here is what I think is happening with yours. The white-light mechanism that lifts the 3 cam plates upward moving the filters out of the light path is a clever design, but the design is crudely executed.

    By experimenting, I found that I could engage the white-light lever and then return it to the “normal” position—except that the mechanism binds in the slightly raised position. This holds the filters’s cam followers at least partly off of their cams, and, therefore, not fully engaged as the numbers on the panel indicate.

    Then with a slight touch or vibration to of one of the knobs, the lever, or even no touch at all, the springs can unexpectedly move the white light cam plate fully back to the neutral position. The springs on the filter plates then snap the filter plates back down until the follower rods seat back onto their respective cams. Of course there is an abrupt change in filtration when this happens.

    If this is the case—and I’m hoping that it is, as it’s the only solution that makes sense—then all you need do to prevent this from happening again is to make sure that the white-light lever is fully into its neutral (horizontal) position, and from then on, use only the filter knobs to move the filters. Don’t touch the white-light lever, as it’s unreliable and can spoil the settings by hanging up as I’ve described.

    There is nothing to be gained by installing coil springs or elliptical spring washers and attempting to do so might wreck something. For example, you might have to apply a great deal of force to get a knob off and break it, bend the front panel, or break one of the cams. I don’t think that replacements are available. Even if they are, they’d be difficult to install and expensive. Any such tampering will gain you nothing.

    Other than this annoying foible, the Chromega C760 is a decently made dichroic head and should give good results for many years. If you get really attached to this machine as I have become attached to my B66XL Dichro, then it might be prudent to look around eBay to find another clean C760 dicho head as a spare.


    Angry Kitty replied by PM on Saturday, February 5

    “So it turns out you were right about the white light lever.... I didn't use it for a bit and nothing happened, then when I started again I noticed the dials were moving up. No ghost after all!”
     
  12. angrykitty

    angrykitty Member

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