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  #1  
Old 22nd October 2017, 12:15 AM
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Thumbs down Chinon CP-9AF SLR

Hello, all, and Autumn greetings from the Pacific Northwest.

I have been going mad lately, buying too many film cameras. All my SLRs are k-mount so when I saw a Chinon CG-5 for sale in a thrift shop for $7 I bought it. I liked it so much that I began researching Chinon SLRs and subsequently have acquired two Chinon CP-9AF cameras.

One of the latter has a "sticky mirror" problem. That is, after an exposure the mirror will not instantly return to the viewing position. After a delay of a few seconds the mirror will behave correctly. I think the problem is caused by a poor contact between the 28-70mm autofocus lens's gold-plated contacts and the mating contacts in the throat of the camera. (Clue: When I put a bit of rotational torque on the lens the mirror will recover.) I have cleaned the contacts with alcohol and this has improved the problem a bit. But when it's in the mood the camera goes back to its evil ways.

Can anyone suggest anything I can do myself to fix this annoying behaviour?
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Old 22nd October 2017, 07:04 AM
John King John King is online now
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Almost certainly it is not the electronics at all. It is more likely to be the mechanical hinge that the mirror pivots on.

Canon A1 models were notorious for it emitting a 'groan' when the mirror was descending and was a sure sign it needed a good CLA. A reasonable technician would be able to sort this out quite cheaply. This happens through lack of use but now it has got to this stage, it won't repair itself.

I would not recommend a home 'repair' because the lubricant will be specific for that purpose and the pivot may not be readily accessible to a home mechanic.
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Old 22nd October 2017, 09:06 AM
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There's a number of reasons why a mirror may stay up. One often quoted reason, though I've never seen it, is the mirror buffer foam becoming sticky and literally sticking to the mirror. Maybe worth checking but I think it's unlikely.

If this were a Contax I'd say you have a slipped mirror and the mirror is binding against the back of the lens, hence why, when you jiggle the lens, the mirror returns. But I don't know if it's possible for the mirror to slip in a Chinon. Worth checking though especially if you have another you can compare with. If the problem only happens with the lens attached this could also indicate this as the problem.

It could also be a problem with the mirror mechanism and the mirror is not getting released. Could be just a matter of lubrication but I wouldn't go squirting oil anywhere unless you know for sure what you're doing.

It could also be a shutter problem. If the second curtain doesn't complete its travel it won't release the mirror. As you have another to compare with, try looking at the shutter when the mirror has become stuck to see if it is in a different position to the shutter on the working one. The difference may only be very slight.
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Old 22nd October 2017, 11:34 AM
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It could be something as simple as the foam the mirror bumps up against when it flips up out of the way getting gooey and sticky. Sometimes the mirror gets stuck up momentarily before falling back down.


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Old 22nd October 2017, 06:12 PM
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Quote:
Originally Posted by Brock View Post
It could be something as simple as the foam the mirror bumps up against when it flips up out of the way getting gooey and sticky. Sometimes the mirror gets stuck up momentarily before falling back down.


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Thanks for your suggestion but I did check the damper foam earlier. There is no evident tackiness. Furthermore, when I operate the shutter with no lens present the mirror operates flawlessly, without hesitation of any kind. The problem only occurs when the lens is mounted.
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Old 22nd October 2017, 06:15 PM
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Quote:
Originally Posted by John King View Post
Almost certainly it is not the electronics at all. It is more likely to be the mechanical hinge that the mirror pivots on.

Canon A1 models were notorious for it emitting a 'groan' when the mirror was descending and was a sure sign it needed a good CLA. A reasonable technician would be able to sort this out quite cheaply. This happens through lack of use but now it has got to this stage, it won't repair itself.

I would not recommend a home 'repair' because the lubricant will be specific for that purpose and the pivot may not be readily accessible to a home mechanic.
Thanks for your suggestion. However, when I operate the shutter with no lens present the mirror operates flawlessly, without hesitation of any kind. The problem only occurs when the lens is mounted. This suggests to me that there is not a mechanical problem with the mirror mechanism.
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Old 22nd October 2017, 06:18 PM
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Quote:
Originally Posted by Roy in Silver View Post
Thanks for your suggestion but I did check the damper foam earlier. There is no evident tackiness. Furthermore, when I operate the shutter with no lens present the mirror operates flawlessly, without hesitation of any kind. The problem only occurs when the lens is mounted.
Is the mirror mounted correctly? Is it hitting the back of the lens?
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Old 22nd October 2017, 09:09 PM
monopix monopix is offline
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Quote:
Originally Posted by monopix View Post
There's a number of reasons why a mirror may stay up. One often quoted reason, though I've never seen it, is the mirror buffer foam becoming sticky and literally sticking to the mirror. Maybe worth checking but I think it's unlikely.

If this were a Contax I'd say you have a slipped mirror and the mirror is binding against the back of the lens, hence why, when you jiggle the lens, the mirror returns. But I don't know if it's possible for the mirror to slip in a Chinon. Worth checking though especially if you have another you can compare with. If the problem only happens with the lens attached this could also indicate this as the problem.

It could also be a problem with the mirror mechanism and the mirror is not getting released. Could be just a matter of lubrication but I wouldn't go squirting oil anywhere unless you know for sure what you're doing.

It could also be a shutter problem. If the second curtain doesn't complete its travel it won't release the mirror. As you have another to compare with, try looking at the shutter when the mirror has become stuck to see if it is in a different position to the shutter on the working one. The difference may only be very slight.
Seems I'm the only one who can see my posts. Strange.

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Old 22nd October 2017, 10:00 PM
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Sounds like contact between mirror and lens. Have you tried another lens? The problem could be either the lens, or the mount on the camera. I once bought a Nikon F3 body which had a damaged mount. I only realised when I fitted a lens. It was more difficult than normal. A close look showed that the mount was seperating from the body, probably due to a heavy lens being used unsupported. I got a refund from the shop. If your mirror drops when twisting the lens, it sounds like you are effectively removing an obstruction.
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Old 22nd October 2017, 10:20 PM
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Quote:
Originally Posted by alexmuir View Post
Sounds like contact between mirror and lens. Have you tried another lens? The problem could be either the lens, or the mount on the camera. I once bought a Nikon F3 body which had a damaged mount. I only realised when I fitted a lens. It was more difficult than normal. A close look showed that the mount was seperating from the body, probably due to a heavy lens being used unsupported. I got a refund from the shop. If your mirror drops when twisting the lens, it sounds like you are effectively removing an obstruction.
Alex


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I did indeed try it with another lens and the problem was still evident. I shall inspect the mount as you suggest. The funny thing is that when I remove the lens and, in desperation, buff up the contacts on both lens and mount, the problem is usually, although not always, fixed. Then after a few actuations of the shutter the mirror's slowness to recover is again evident.
I shall do some more investigation and report back. Thanks again for your help!
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