Rb67 Prism finder repair

Discussion in 'Medium Format' started by mark4583|1, Jan 23, 2021.

  1. Do you know if I have to take this completely apart to get to this or how does this come apart, My problem is it works fine, its the indents that wont hold the wheel in place and it easily moves from 1 Asa to another, some of the higher Asa setting do have the indents to hold the wheel. Would like to take a peek inside to see if it just needs a little cleaning or repair.

  2. The indent might loosen with lighter fluid dribbled down inside the wheel. The indent could be fouled with gunk. You would need to lay the finder over at an angle after dropping the lighter fluid in to prevent fluid going further into the finder

    It's hard to know how the wheel could be dismantled but the silver "hub" may be a screw that screws out. If it has index marks on it, they would have to correctly aligned when the screw is replaced. I'm only guessing about all this because I can find nothing in search results about disassembly. It's just food for thought.
  3. me either, been looking for some time now, even in the repair groups on FB had no answer, I will try the fluid, thanks
  4. It does come apart by turning the chrome knob counter clockwise, was a easier fix than I thought, its just simple tangs that where bunt up where the pin was not fitting between the tangs, I just simply flatten the tangs back , and all works great now. I was half expecting a spring to shoot out and parts fly every where! lol

    prismwheel.jpg prismwheel2.jpg
    mag_miksch, kmac and orsetto like this.
  5. Congrats on the repair! :) I figured that silver knob must unscrew somehow, but couldn't find my disused TLR porrofinder to verify.

    For future reference, its may be useful to note here that Mamiya employed essentially the same control dial in multiple contemporary CdS finders: this RB prism, the RB CdS Rigid/Mag Hood, the TLR CdS Porrofinder and TLR CdS Rigid/Mag Hood.
  6. Great job, glad the screw came out for you. Some lubrication on the underside of the tangs and indent pin plus it's spring would help with the longevity of the dial unit. Perhaps a smear of lithium grease.
  7. Glad you got it fixed.
  8. it has a spring under the plate and under the knob.

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