Switch to English Language Passer en langue française Omschakelen naar Nederlandse Taal Wechseln Sie zu deutschen Sprache Passa alla lingua italiana
Members: 70,571   Posts: 1,545,551   Online: 1094
      
Results 1 to 5 of 5
  1. #1

    Join Date
    Nov 2009
    Location
    Capital of Oregon Territory
    Shooter
    Multi Format
    Posts
    776

    What is the replacement Photodiode for Mamiya 645 PD prism?

    I'm trying to repair my newly acquired Mamiya 645 1000s camera with PD prism. The prism was showing rather erratic
    measurements which I traced down to one cracked photodiode in the prism. I'd like to replace the photodiode, but I don't see any markings on it. It is a small black rectangle about 6x8mm with two golden wires sticking out of the back. Does anyone know what would be a good replacement for this photodiode, and/or maybe have a spare on hand? Also, does anyone know which one of the 5 pots in the prism should be used for calibration? From the circuit, I can guess it's one of the two near the top of the prism that feeds reference voltage into the op-amp. However, I'd rather not touch them until I'm sure.

    Thank you!

    Eugene.
    P.S. Yes, I know, I can buy another prism for not a lot of money. However I hate to throw away a perfectly repairable unit, at least not until I totally destroy it in my repair attempts
    Last edited by anikin; 03-10-2014 at 02:37 PM. Click to view previous post history.

  2. #2

    Join Date
    Jul 2013
    Location
    Michigan
    Shooter
    Medium Format
    Posts
    137

  3. #3

    Join Date
    Nov 2009
    Location
    Capital of Oregon Territory
    Shooter
    Multi Format
    Posts
    776
    Quote Originally Posted by wombat2go View Post
    Thank you for the link. However, I'm not sure what I should be looking at on this page. The photodiode I'm looking for is similar to FDS10X10, but much smaller. Mouser has a few that look similar, but they all are larger than the one I'm looking
    for.
    I wish I knew the component name for it, then at least I could start looking for a replacement with similar wavelength/sensitivity characteristics.

  4. #4

    Join Date
    Nov 2009
    Location
    Capital of Oregon Territory
    Shooter
    Multi Format
    Posts
    776
    Ok. Since nobody wanted to tell me, I'll reply to my own question. I could not find the exact replacement, but I found a very similar diode at alliedelec.com. It is VTB8440BH ceramic photodiode. It is just a bit taller than the ones inside of the prism. I had to shorten it a bit by sanding off the rounded ends. After that, the diodes fit perfectly. And most importantly, the meter now reads precise exposure, and I did not even need to recalibrate it! Success!

    Eugene.

  5. #5

    Join Date
    Jul 2013
    Location
    Michigan
    Shooter
    Medium Format
    Posts
    137
    Well done.



 

APUG PARTNERS EQUALLY FUNDING OUR COMMUNITY:



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