Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,499   Posts: 1,543,219   Online: 1059
      
Page 1 of 2 12 LastLast
Results 1 to 10 of 15
  1. #1
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,216

    Minolta MOD III Lamp/Power Modification

    Back in the late 70s the voltage regulated 19V power supply for my Minolta Mod III enlarger went bad. I converted it over to a 1/2 wave rectified non-regulated supply with a big diode. It has a 24V transformer, so half of that is around 13 measured volts.

    I used the enlarger like that all these years. Now I letting my kids use that enlarger. The "Kodak Projection Print Scale" works great with kids, they can just pick out the pie that looks good. However, our printing times were not always under 60 seconds with Y/M multigrade filtration dialed in.

    So, I decided to look into optimizing the light output.

    The enlarger has used the EKG bulb all these years. That is the original type bulb and it is rated at 80W at 19 volts. Well, since I only have 13 volts, I thought a 12 or 13V lamp would get me back to optimum intensity.


    A search of various bulbs led me to the DED bulb. It is 85W at 13.8V with the same GX5.3 2-PIN base. Cost about $5.00. It is on order, but I'll post my results when it arrives.

    Last edited by ic-racer; 12-06-2009 at 04:10 PM. Click to view previous post history.

  2. #2

    Join Date
    Mar 2014
    Shooter
    35mm
    Posts
    5

    Mod III power supply options

    Any suggestions of how to fix a power supply?
    Blown the circuit board after my unit was in storage for many years.
    Cannot find replacement boards from OEM.
    Does not have schematic to fix circuit board.
    Any advises??

  3. #3
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,216
    Quote Originally Posted by kinghl View Post
    Any suggestions of how to fix a power supply?
    Blown the circuit board after my unit was in storage for many years.
    Cannot find replacement boards from OEM.
    Does not have schematic to fix circuit board.
    Any advises??
    You can easily half-wave rectify the voltage from the 24V transformer with a large diode. That is how my unit was repaired in the 1970s by Minota service. Subsequently they re-engineered the power supply that shipped with new enlargers.

    I wound up buying a power supply with the newer circuit from an APUG user. How do you know if you are buying a newer circuit power supply? Easy, if it is still working it is probably the later version

    Another thread here: http://www.apug.org/forums/forum43/1...olor-head.html
    Last edited by ic-racer; 03-09-2014 at 12:54 PM. Click to view previous post history.

  4. #4
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,216
    There is a minolta power supply on ebay now for $30 but the text reads " I am not a professional on how it really works." which usually means it is broken and does not work.

  5. #5

    Join Date
    Jul 2004
    Location
    fairfield county, Ct.
    Shooter
    Large Format
    Posts
    1,817
    Images
    24
    best small frame enlarger I ever used!! someone should start production of these again...
    best, peter
    website down for maintenance!

  6. #6

    Join Date
    Mar 2014
    Shooter
    35mm
    Posts
    5
    Do you have the specifications of the 24V transformer and the diode?
    Your description really does not tell me how to get component and how to put it together.
    Like to get my unit working so I can sell it to someone who really can use it.

  7. #7
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,216
    Quote Originally Posted by kinghl View Post
    Do you have the specifications of the 24V transformer and the diode?
    Your description really does not tell me how to get component and how to put it together.
    Like to get my unit working so I can sell it to someone who really can use it.
    If the term "half wave rectification of 24V to 12V with a diode" does not make sense to you then this procedure will be difficult and perhaps dangerous. The primaries of the transformer are 120V which is lethal voltage.

    Having posted the above, lets start from the basics. Do you have a soldering gun? If so then maybe you have an extra diode laying around. Diodes are rated per reverse voltage. If you have a 1N4001 (35v) that should do but if you need to buy one you could get a 1N4002 (70V) to have more of margin against failure.

    The principle of half-wave rectification is described here: http://web.physics.ucsb.edu/~lecture...ges/64.57.html

    You need to find the secondaries of the transformer and connect the diode between one wire from the transformer to the lamp.

    After the procedure the device is no longer UL or CE approved. You may want to take that into consideration if you are going to sell it.

  8. #8

    Join Date
    Mar 2014
    Shooter
    35mm
    Posts
    5
    Are you referring to the original transformer in the power supply?
    Use the diode to by-pass the circuit board straight 12 v to the lamp?

  9. #9
    ic-racer's Avatar
    Join Date
    Feb 2007
    Location
    Midwest USA
    Shooter
    Multi Format
    Posts
    6,216
    Yes, the transformer in the box should be a 120V to 24V transformer if I recall correctly. The circuit board electronics are not used after the procedure.

    You could also look up the Beseler 23C III color head with "built-in solid state power supply" which I believe is just a rectifying diode (part #90).
    Last edited by ic-racer; 03-11-2014 at 09:38 PM. Click to view previous post history.

  10. #10

    Join Date
    Mar 2014
    Shooter
    35mm
    Posts
    5
    I remember (over 30 years ago) when I bought this, the ads said the power supply has "stabilized" feature to minimize lamp variation.
    Does the original circuit board suppose to do that? If the circuit board is by-passed, what effect will that have to the variation of the lamp?

Page 1 of 2 12 LastLast


 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



Contact Us  |  Support Us!  |  Advertise  |  Site Terms  |  Archive  —   Search  |  Mobile Device Access  |  RSS  |  Facebook  |  Linkedin