Converting Super Chromega II to 120V

Discussion in 'Darkroom Equipment' started by ic-racer, Oct 31, 2009.

  1. ic-racer

    ic-racer Member

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    This project is about fixing up a surplus Omega Super Chromega II head without power supply.

    The plan is to eliminate the power supply and plug straight into a standard timer.

    If all goes as planned I'll probably donate to a local fellow APUG user that is just starting a darkroom.

    Many thanks to BobNewYork for donating the Chromega for this project.
     
  2. ic-racer

    ic-racer Member

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    Without a power supply, what is missing?

    Well, the bulb is 24v and the 'standard' power supply ( 412-021) is just a box with a 24v transformer. I can get a 10A 24v transformer from mouser for about $12, but then I'd need a box and a 6-pin female connector and some AC sockets. Alternatively, I could seek a busted power supply for free or $10 and just use the box and the sockets.

    Perhaps the cheapest way is to try and change the bulb to a 120V bulb.

    The specs on the original bulb are:
    ELC

    BASE:GX5.3

    WATTS:250

    VOLTS:24
    MR16 Halogen

    It happens that the EXX
is 250W and has a GX5.3 base. It runs from 120V

    So, it seems that bulb can just plug right in.

    All I need to do is wire a cord straight to the bulb.
    Then, remove the cord with the 6-pin connector and wire a second cord for the fan and utility lamp.
     
  3. Bob-D659

    Bob-D659 Member

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    The fan in the Chromega head unit off a D5XL that I have is 120 vac. I didn't check the wiring for the small bulbs.
     
  4. ic-racer

    ic-racer Member

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    Yes, and it looks like the small bulb is 120VAC also.

    I just opened it up and even though there is a 6-pin connector on the end of the cord, it is a 4 wire cord:

    Green = Ground
    Black = Hot 120 VAC
    Red = Hot 24VAC
    White = Common

    The wires go to a buss bar using spade connectors. Things are a little tight because the fan is right there.

    To re-wire it would involve running two 3-wire cords and re-doing some of the spade connectors so it would be theoretically a reversible modification, or at least look like factory-original wiring. Though, I will need to make an additional hole in the chassis.
     
  5. ic-racer

    ic-racer Member

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    Fan: gets one wire from Black and one wire from White
    Small bulb: gets one wire from Black and one wire from White (though both wires going to the bulb are physically black).
    Main Bulb: gets one wire from White and one wire from Red.
     
  6. ic-racer

    ic-racer Member

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    Some mechanical problems to manage:

    Rear panel caved in like it was dropped.
    Some numbers are worn off the number wheels.
    All the foam is gone.
    Magenta does not 'zero.'
    Small bulb is gone.
     
  7. ic-racer

    ic-racer Member

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    Now if I can find some batteries for my "D" camera I'll post some pictures.
     
  8. Mike Wilde

    Mike Wilde Member

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    My chromega head refurb efforts

    my comments are buried in the quote above
     
  9. Steve Smith

    Steve Smith Subscriber

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    Or a diode if you are running on AC. Something like a IN5404 will do. A resistor will dissipate the same power as the bulb and will get hot a diode will not.


    Steve.
     
  10. Neal

    Neal Subscriber

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    Dear ic-racer,

    I actually modified an old Chromega head once. I'm pretty sure you will need a different socket for the 120V bulb. They are pretty easy to come by. Everything else is pretty straightforward.

    Neal Wydra
     
  11. ic-racer

    ic-racer Member

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  12. ic-racer

    ic-racer Member

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    The main problem was the dichroic filters and levers.
    I took the assembly apart and cleaned everything.
    The dichroic filters were in good shape and needed to be re-guled to the lever arms. I used silicone glue.
    [​IMG]
    [​IMG]
     
  13. ic-racer

    ic-racer Member

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    The stacks of separating washers were different at the pivot and the sliding ends of the moving filter levers. This was rectified.

    The springs were buggered and they were straightened at the ends and put on the correct hooks, so they don't interfere with each other.
    [​IMG]

    [​IMG]
     
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  15. ic-racer

    ic-racer Member

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    The number counters were not making contact with the filter wheels. This was easily rectified.

    Some of numbers are rubbed off (How, unless someone kicked this thing around on the ground without that cover plate in place????)

    [​IMG]
     
  16. ic-racer

    ic-racer Member

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    The back panel was straightened and re-painted in a few areas.

    [​IMG]
     
  17. ic-racer

    ic-racer Member

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    Here is the finished product. Well, almost finshed. I need to do the foam light seals, but I'll wait until I get if fired up so I can test the seals as I go.

    I re-painted the numbers by hand with white enamel and a 000 brush (Hey, I do have an art degree, after all).

    [​IMG]
     
  18. ic-racer

    ic-racer Member

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    The small bulb is a 6s6, I found one place that has them for $0.97

    Product/ANSI Code#: 6S6/DC 120V

    WATTS:6

    VOLTS:120

    EI PC#:40804

    PH#:373761
SY
    PC#:16782

    GE#:11592
BASE:BA15d
     
  19. ic-racer

    ic-racer Member

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    OH, wait, what about the 120V conversion???

    Well, after thinking it over, I thought it best to do the conversion in a separate box, like the original power supply. This would allow the use of the original single cord that exits the lamphouse. Things are so tight in the head that extra wires could be problematic. Also, by keeping the head original (except for the bulb), it could easily be hooked up to the correct power supply if needed.
     
  20. ic-racer

    ic-racer Member

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    The ideal conversion box will be a trashed power supply, as it will have the appropriate 6 pin connector. Anyone out there have one?

    Also, a 24v transformer can be had for like $10, so it might be worthwhile to just go ahead and put a transformer in my box. I'll see what kind of a box I can come up with.

    The ELC bulb is about $10 wheres the EXX bulb is $20. So, in the long run it might be actually cheaper to buy the $10 transformer and use the cheaper 24v bulb.
     
  21. ic-racer

    ic-racer Member

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    Also, I took the mixing box apart and inspected it. It seemed OK, only a slight yellowing. The the diffusion plastic was quite dirty. I cleaned this well and re-assembled the box.
     
  22. Erik L

    Erik L Subscriber

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    Hey Ic, that looks like it would fit my d5xl perfectly, I wish I had one:smile: I never new they were 220 v. good work.
    erik
     
  23. ic-racer

    ic-racer Member

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    Ok, so it looks like someone from the large format forum is going to pitch in a burned out chromega power supply. So my plan at this time is to use that Chromega box and put the $10 Hammond 24V 10A transformer (from mouser.com) into the box.

    I'll post the progress...

    BTW this head and power supply are getting donated to be put on an Omega D3 that was donated by fellow APUG users for a friend that is starting a 4x5 darkroom from scratch. Kind of a community project. Thanks to everyone that has pitched in!
     
  24. ic-racer

    ic-racer Member

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    Well, I made a mistake on my power calculations for the transformer. The $10 transformer is ten times too small. The size I need is in the $75 to $130 range. I need 120V input and 24V output and 250VA rating (not 10VA as I had initially calculated).

    So, I'm looking at a transformer like this for about $80: http://www.mouser.com/ProductDetail...GAEpiMZZMv4oUrzpPKU3A2NOXuypJmAfCky0uhE%2brE=

    Now things have shifted in the other direction, looking like the $20 bulb that runs from 120V might be a more cost effective solution.
     
  25. bdial

    bdial Subscriber

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    You could use a household dimmer. Hook it up to the head, or an equivalent load (better maybe, probably easier), move the slider 'till you get to 24 volts. Mark the position or super glue it in place. The method worked well for me as a temporary solution to a failed enlarger power supply.
    I used one that had an on-off switch separate from the dimming slider.
     
  26. ic-racer

    ic-racer Member

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    Interesting solution. So instead of a transformer, usa an inexpensive triac circuit to chop the waveform.