Finding a light leak in RB Pro-S system

Discussion in 'Camera Building, Repairs & Modification' started by tkamiya, Dec 3, 2011.

  1. tkamiya

    tkamiya Member

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    I just acquired a Mamiya RB Pro-S system and film tested it. Unfortunately, there are light leaks.

    I found a source of one leak because it appears on every frame at fixed distance from each frame. There was a seal a tad too short - obviously an attempt to fix by previous owners. I think this one would be a simple fix.

    More difficult to track down are two other issues.

    As part of my testing, I inserted a dark-slide and unmounted the back. Then I let the opening (still closed) face direction of sun for few seconds. When I did this, that particular frame had a faint fuzzy leak around the perimeter of the frame. I think it means a leak from frame opening and the dark slide itself.

    Also, when each time I rotated the back, there were additional leak - kind of faint but it's there. It appears as a bar exactly half way between the frames all the way across the width of the film. This is less troublesome because it's entirely outside the frame.

    Here are couple of questions. I ask these because RB are an popular model here on APUG and I'm pretty sure there is quite a knowledge accumulated already.

    1) Are these pretty much known issues with known fixes?
    2) I can replace seals but other than wasting a roll of film each and every time to test, is there a trick?
    3) I'm thinking rotating back is not the cause of this problem? The seal appears intact. Plus, when I rotate, I grab the back. I can see how it can distort the back itself just enough so that weak seal might leak when I do this.

    I have number of options. I bought this kit from a reputable place and I'm sure I can exchange it. But, because of the age of the equipment, I hate to keep getting new ones and keep testing, wasting a roll each time. I would very much like to have my options lined up before I contact the seller.
     
  2. agfarapid

    agfarapid Subscriber

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    My advice--get an exchange. I have an RB Pro S purchased used on the auction site. Had to replace the light seals on the magazine back but that's about it. With so many RB's on the market it doesn't make sense to go through the hassle of repairs. Just my 2 cents!
     
  3. CGW

    CGW Member

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    The main culprits are usually the back and RB adapter. The backs are old enough to have issues. The chief sources of leaks are at the hinge and clasp of the outer shell. Another area is the surface and seal where the back meets the RB adapter. There's a shallow channel surrounding the film gate that takes a seal that's often shot. These are DIY jobs with thin adhesive-backed foam from a craft store. The eBay kits are expensive and overkill for this job. Getting the old gooey foam out is the biggest pain. I've done several RB 67 Pro S backs and bodies that were NOS but had decaying seals with no subsequent issues. Get some thin black foam sheet, an Xacto knife, and a metal straight edge. Isopropyl 99% and a popsicle stick whittled to a chisel edge work great to great the old foam out quickly and intact.

    Here's a rough guide to what's where on the similar but earlier RB67. I'd stick to the film back and RB adapter and leave the body alone:

    http://aki-asahi.com/store/html/Mamiya-RB67/Light-seal/index.php
     
  4. tkamiya

    tkamiya Member

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    Thanks both. I tend to agree with both. I'm going to call the seller (well know used camera dealer) for an exchange.

    CGW, how do you test your back? Do you waste one roll each time or do you have a trick? I'm thinking of cutting 120 roll in half and make two rolls out of one for this purpose.
     
  5. CGW

    CGW Member

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    Dude, it either leaks or it doesn't. Get some outdated crap 120 and try it, before and after a seal job. Too intense? Then just go for the refund. Be advised, though, that Pro and Pro S bodies and backs will likely have problems--it's an age-related thing.
     
  6. paul ron

    paul ron Member

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    With the lens off, put a bright light inside the camera, turn th elights off n inspect it.

    Seals n bellows are the most common leaks.

    Get a seal kit form Goodman Interslice. If it;'s the bellows, you'll have to either get the exchange where you bought it, or have it replaced by a tech.

    .
     
  7. tkamiya

    tkamiya Member

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    Let's see what shows up tomorrow.... I returned one and bought two. Hopefully at least one is leak free....

    paul ron,
    The bellows looks brand new. I actually found the source of at least one leak. On the film back, one of the sealing material in channel was a bit too short allowing the light to leak in. Putting the processed film right up against the pressure plate, the leak perfectly lines up with this gap in seal. I know about Jon Goodman. I'm in contact with him already but thanks.
     
  8. tkamiya

    tkamiya Member

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    Grrrr.... second set (I bought two) backs still leak light at different degrees and at different places. Now it's certain it's the back that's leaking.

    I might just forget -S back and go to -SD back as they don't use seals.