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Author Topic: Petri 7S, first shot slow shutter  (Read 1287 times)
ImageMaker
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« on: June 06, 2006, 09:52:31 AM »

I've got this Petri 7S that titrisol gave me about a year ago.  I thought I had it fixed then, with a shutter cleaning and a piece of foam to seal a light leak around the door hinge, but since then I've noticed that the first exposure after the camera sits, cocked, for a while (anything from a few hours up) is very, very slow, similar to what I get with a manually cocked shutter if I retard the cocking lever with a finger when firing the shutter.  I thought this was due to congealed grease on the cocking transfer bar (the one that goes "clunk" when you advance the film), so I cleaned that and applied some teflon grease, then after a bit cleaned it again and left it dry (or at least with just the very minimum film of teflon that's almost impossible to remove after using the Permatex Superlube).

Still does it.

I've suspected this might be due to more of the congealed grease between the cocking ring and the body, but I've been reluctant to try to get that deep again; the meter cell in a ring around the lens, and its wiring to the galvanometer movement in the top plate, mean unsoldering and resoldering wires in order to separate the lens and shutter layers from the body, and the last time I did this I melted a plastic insulating collar and had to replace it with a piece of silicone tubing.  So, I'd like to try to be reasonably sure that's the problem, or verify if there's another way to get to that cocking ring.

I have the service manual for the camera, but it's written to provide reference for a trained technician, not to give instructions to someone who's only had a few cameras apart aside from shutters that aren't really connected to the camera body mechanisms.
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Glenn Thoreson
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« Reply #1 on: June 06, 2006, 12:30:18 PM »

Ye shouldn't let the camera sit with the shutter cocked. It be bad for it.
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Glenn from Wyoming

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« Reply #2 on: June 06, 2006, 07:08:57 PM »

So -- are you telling me this is a spring relaxing, but it's fine three seconds later after I recock the camera?  If so, the camera can't be relied on for certain kinds of photography -- like those where I might need to have it ready for considerable time to catch a shot that won't give time to cock before exposing (not to mention the noise of the transfer bar slamming home at the end of the advance stroke).

I've been assuming it was grease, because it seems worse in cooler conditions and better when the camera is warmer...
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MichaelHarris
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« Reply #3 on: June 07, 2006, 01:30:48 AM »

Steel can do funny things, especially when it's been stretched for a really long time.  I don't know alot about camera repair but I don't leave any of them cocked.
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Dean Williams
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« Reply #4 on: June 07, 2006, 10:51:19 AM »

Quote from: ImageMaker

I've been assuming it was grease, because it seems worse in cooler conditions and better when the camera is warmer...


I think you're on the right track with this, Donald.  I get a lot of shutters here with the customer's complaint that the shutter fires slowly the first shot or two.  Then it will get better until it sets a while.  
I don't remember what the Petri has for a shutter.  If it's their own design, it's probably a type of Prontor copy.  That's  usually going to be oil on the blade actuator ring, or the mainspring shaft will have a little sticky grease/oil on it.

Sometimes when I have to remove a "ring around the lens" cell to get to a shutter, I snip the wires at a mid point and then add a little extra wire when I re solder.  I have some very small gage wire and srink tube if you need some and want to try this.
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Dean W
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Glenn Thoreson
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« Reply #5 on: June 07, 2006, 11:12:16 AM »

Sounds like goo to me, too. I still don't like to leave them cocked unnecessarily.
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Glenn from Wyoming

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Dean Williams
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« Reply #6 on: June 07, 2006, 12:07:01 PM »

No, I don't think it's a good idea either, Glenn.  I've seen where some folks say a spring never wears out, but that's hogwash.  The way I see it, if they can break (they can) they can wear out.  Compression sprngs are probably less affected by being constantly loaded, but most springs in a shutter are to provide torque or are extension springs.  I think they are better off left at rest for long periods storage.

I think shutters can probably go cocked for longer than most of us think though.  I've had a number of cameras come to me for repair where the owner said the camera quit working "three years ago" and now he wants it fixed.  It will have been cocked when it quit working and sit on a shelf since.  Most come back to life after a good cleaning.  Some though, will run a bit slow forever after.
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Dean W
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Glenn Thoreson
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« Reply #7 on: June 07, 2006, 05:59:25 PM »

Is that a leaf shutter on the Petri? I find that, often, it's caused by gunk between the blades on leaf shutters that causes this. Often, you can't see it unless the blades are partially open. It can look perfectly clean when closed. After it sits a while, the blades will start to stick toogether. Of course, if it has a focal plane shutter, just keep this in the back of yer mind and apply it to something else.
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Glenn from Wyoming

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« Reply #8 on: June 07, 2006, 07:31:30 PM »

Glenn, I just checked -- the camera has been sitting for 2-3 days since I last picked it up, and was NOT cocked.  I cocked it, and fired, with shutter set to 500 -- and it took most of 1/2 second to eeeeease open, and then leisurely close, that first time (house is about 68-70 F with the A/C running).  Second shot was perfectly normal.

Yes, it's a leaf shutter -- this is a fixed-lens RF camera, no reason for a focal plane.  There's no brand on the shutter other than Petri, and I haven't had enough shutters open to be able to say "yes, it looks like a Prontor inside" or "no, this is a Seikosha copy" or "silly, this camera has a unique design."

For springs, my understanding has been that unless the spring is overstressed in design, modern materials don't weaken.  Mainsprings in guns used to weaken over time (some of the earliest versions of the Colt 1911 had this problem -- if carried "cocked and locked" for a few years, they might start to misfire because the hammer wouldn't strike the firing pin hard enough), but they didn't recover when left untensioned for a while.  If you bend a spring beyond its elastic limits, that's another story, but at anything resembling normal temperatures, a modern steel spring won't creep, weaken, or take a permanent set within its designed range of movement.  I'll continue to leave my Speed Graphic at T and tension 1, because who knows what the steel was like in 1939, but I don't worry much about my post-War shutters -- and this is the only one I have (in current service, anyway) that cocks when I advance, other than my Spotmatic, and both of those are new enough designs it shouldn't be a problem.

Anyway...

Gunk it is, then.  Ideally, I'd like to completely remove the shutter from the camera and clean it, then, but alternately, if I can find some money, I'd be willing to pay something to get someone else to do it.  I pretty well have to work in "single sitting" mode, because my work space is the same table I eat meals at, so I can't leave a camera spread out in pieces while I think about stuff or soak parts or whatever.

Question is, how do I get the shutter completely off this camera?  I presume I'll need to remove the front bits like I did last time, including unsoldering the meter wires, and then use a "special spanner", according to the manual, to remove the retaining ring from inside the back -- with very little clearance, and hardly any room to work, without scratching up the rear lens.

Dean, if you're interested in a CLA job, PM me... Tongue
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connealy
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« Reply #9 on: June 07, 2006, 08:00:03 PM »

Quote from: ImageMaker
Glenn, I just checked -- the camera has been sitting for 2-3 days since I last picked it up, and was NOT cocked.  I cocked it, and fired, with shutter set to 500 -- and it took most of 1/2 second to eeeeease open, and then leisurely close, that first time (house is about 68-70 F with the A/C running).  Second shot was perfectly normal...
I think Glenn has it; that is pretty typical of dirty shutter blades.  If you can take out the lens groups, you can probably fix it by swabbing the blades with some Ronsonol, and then carefully scrubbing it off with some q-tips.  Keep at it until they are clean.
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« Reply #10 on: June 07, 2006, 08:51:02 PM »

Mike, that's exactly what I did the first time I was into this shutter (about a year ago); before that, the camera didn't work at all, wouldn't even advance because the actual shutter trip (not just the release movement) is required to unlock the film advance.  However, I wasn't able to access the back surface of the shutter, and though that looks clean through the back of the lens, there could easily be stuff there that washed in from the front.

I'll check the manual again -- if the shutter comes out with just removal of the retaining ring I can see inside the back, I should then be able to remove the rear lens and finish the job.
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Wimpler
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« Reply #11 on: June 07, 2006, 11:59:29 PM »

I think you may actually have to take the shutter blades entirely out of the shutter.
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ImageMaker
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« Reply #12 on: June 08, 2006, 08:37:56 AM »

You might be right, Wimpler, but if that's required with this shutter, I'll either save up the money to send it out, or sell the camera in "needs CLA" condition.  I've been in there once, and I'm pretty confident of my *inability* to split the shutter, remove and clean the blades, and get everything back in and working again.
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