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Bettersense
Tinkerer
Username: Bettersense
Post Number: 1
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 16, 2008 - 12:51 am: | 
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I recently inherited a Canon AT1 in great-looking condition with what appears to be the kit lens. After making a silver-oxide replacement battery out of button cells and shrink tubing, it seems to work, and the metering is spot on, but about 10 percent of the time the shutter doesn't seem to work right, resulting in some pretty neat looking photographs with scorched edges, or mostly, the right-third of the photo being a bit over exposed, sometimes also featuring beautiful red auroralike ribbons all over the place.
Since I also vaguely remember experiencing weird shutter lag when these photos were taken, I assume it's the shutter. The mirror cushion foam has all deteriorated and gets on the mirror sometimes, so it's possible that it has gotten in something and gummed it up. The shutter works when it works though, even up to 1000. So I would really like to get it working.
Do you know where I could find exploded diagrams? Is there any chance that I could fix this myself? I'm pretty handy with other stuff but never tackled a camera. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 652
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 16, 2008 - 11:00 am: |
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Ooh, that doesn't look good. The Canon shutters are electronically controlled, but there are a few gears in there. I wonder if some of the crud has gotten into the gear mesh on the #2 curtain and is making it hesitate as the lump passes between the gears. |
Bettersense
Tinkerer
Username: Bettersense
Post Number: 2
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 16, 2008 - 01:10 pm: |
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I also found pretty good service manuals here:
http://www.canonfd.com/choose.htm
with troubleshooting info that says for uneven exposure, clean MG3, which is the solenoid that holds shutter 2 open until it's time to shut it. However I don't know how it could or should be cleaned. I took the bottom cover off and everything seems to be pretty much in order. If there is a problem it must be that shutter 2 sometimes doesn't shut by itself properly. As far as I can tell it's spring-loaded shut and MG3 holds it open, but if MG3 was dirty I don't see how that would cause uneven exposure anyway, just over or under-exposure.
I have tried cycling the camera tons of times without film, and I can't seem to duplicate the shutter lagging, or detect any other problem. Maybe I will shoot another roll and see if it fixed itself. Perhaps it just needed used a bit to get things loosened up, after sitting for so long. |
Rick_oleson
Tinkerer
Username: Rick_oleson
Post Number: 653
Registered: 07-2006
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 16, 2008 - 03:53 pm: |
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How are you checking it? The problem is probably not enough to see with the naked eye just looking through the shutter at a light, but if you use a CRT television or monitor as the target this kind of problem should show up very clearly. If you haven't done it before, take a look at http://rick_oleson.tripod.com/index-135.html |
Scanogram
Tinkerer
Username: Scanogram
Post Number: 15
Registered: 04-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 16, 2008 - 03:56 pm: |
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MG3 doesn't cause the problem you are having. I agree with Rick, something is causing the second curtain to hang up toward the end of the travel. You may have worked it out, give another roll a try. As many of these I've worked on, I don't recall a problem like yours. |
Bettersense
Tinkerer
Username: Bettersense
Post Number: 3
Registered: 08-2008
Rating: N/A
Votes: 0 (Vote!) | | Posted on Saturday, August 16, 2008 - 10:04 pm: |
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Ok I shot up two more rolls today, one B&W and one color. It didn't do any weird shutter lag that I can tell, but I'll drop the film off tomorrow. I also ordered a sealing kit from an internet auction website. |
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