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03-02-2011, 10:14 AM   #1
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Pentax 6x7 TTL meter only works with stopped-down metering

Hey guys, I'm the new owner of a Pentax 6x7, and everything looks good on it except for one problem: The meter works fine when I have the lens switched to manual aperture (stopped-down metering) but as soon as I switch it to auto the meter goes dead. From what I've read this is backwards, anybody else heard of this problem? I have the Takumar 75mm f/4.0 non-shift lens if that helps at all. I've also tried taking off and replacing the lens and the meter in the correct order multiple times, but there's never any results.

03-02-2011, 10:20 AM   #2
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Try removing the TTL prism and with an eraser or other means clean the metal contacts on the body that interface with ones on the prism.
03-02-2011, 11:16 AM   #3
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When I removed the prism all the contacts looked extremely clean, but I'll go over them all again when I get home, thanks.
03-02-2011, 04:39 PM   #4
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Take the lens and prism off the camera.
Mount the prism, and then remount the lens.
It sounds like you haven't got the couple chain connected, or else it is broken.
With the prism off, you should be able to see a very fine chain just to the front of the screen.

03-02-2011, 05:04 PM   #5
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I've already tried removing and replacing the prism and lens in the correct order, and I just cleaned the contacts and it's still not working in automatic mode. I don't see any chain hanging down anywhere, and I don't think I broke it, I've always removed the lens before the prism, unless the last owner broke it. Like I said, the meter works fine for stop-down metering, would that still work if the chain was broken?
03-02-2011, 05:55 PM   #6
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QuoteOriginally posted by trip9 Quote
I've already tried removing and replacing the prism and lens in the correct order, and I just cleaned the contacts and it's still not working in automatic mode. I don't see any chain hanging down anywhere, and I don't think I broke it, I've always removed the lens before the prism, unless the last owner broke it. Like I said, the meter works fine for stop-down metering, would that still work if the chain was broken?
Stop down would still work. I don't have my 6x7 handy at the moment so I can't check for you, but there should be, IIRC, a very narrow slot just in front of the screen and there should be a metal tab attached to a fine (really fine) chain. It links to a sliding lever on the meter prism to tell the meter what aperture is set.
If that chain is broken, you will not have open aperture metering.
I'll follow up with you in a day or so with a picture of the top of my 6x7 with the prism off of it to show you what to look for.
03-02-2011, 08:07 PM   #7
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QuoteOriginally posted by Wheatfield Quote
Stop down would still work. I don't have my 6x7 handy at the moment so I can't check for you, but there should be, IIRC, a very narrow slot just in front of the screen and there should be a metal tab attached to a fine (really fine) chain. It links to a sliding lever on the meter prism to tell the meter what aperture is set.
If that chain is broken, you will not have open aperture metering.
I'll follow up with you in a day or so with a picture of the top of my 6x7 with the prism off of it to show you what to look for.
Thanks for all your help man, I was looking where I think the chain would be and I don't see anything loose or hanging. I also forgot to mention that on auto the camera still properly stops down the lens when a picture is taken, so I don't know if that rules out a linkage chain break or not.
03-02-2011, 08:19 PM   #8
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With the prism off and a lens mounted, you can see the chain moving the metering tab on the front of the focus matte when you change the aperture on the lens.

03-02-2011, 11:06 PM   #9
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QuoteOriginally posted by tuco Quote
With the prism off and a lens mounted, you can see the chain moving the metering tab on the front of the focus matte when you change the aperture on the lens.
Alrighty, just tried this and I can see the chain pulling the little lever, so I guess that rules out a linkage chain break. WTF then. I'm heading to New York tomorrow, does anybody know anywhere I can pop by and see if they can diagnose my problem?
03-02-2011, 11:25 PM   #10
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If this fails, I'd say it is your prism. With the prism on and the lens off, you can manually move the meter tab on the chain. On the lens mount at the 11 O'clock position is a lever. You can move that between the 11 O'clock and 1 O'clock position simulating your aperture on the lens.

Aim the camera at a light, look at the metering needle while moving that aperture lever. If the metering needle is not responding, I'd say the fault is with the prism. Is the pin that on the prism that engages that metering tab on the chain all the way to one side when removed?
03-02-2011, 11:43 PM   #11
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QuoteOriginally posted by tuco Quote
Aim the camera at a light, look at the metering needle while moving that aperture lever. If the metering needle is not responding, I'd say the fault is with the prism. Is the pin that on the prism that engages that metering tab on the chain all the way to one side when removed?
Ok so this is kind of weird. I did what you said, but my meter won't even turn on unless the tiny little nub that's located at 3 o'clock on the the lens mount on the body is pressed down. If that's pressed down and then the meter is turned on, pointing at different stuff changes the meter like it should, but as soon as I move the little aperture tab thing the meter just drops dead. I guess it's a meter problem then, but that's really weird haha.
07-27-2011, 11:34 AM   #12
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I am having the same problem!! When I press the "nub" that is at the 3 o'clock position on the lens mount the meter starts doing its job. I have been trying to fix this problem for some time now so this is great progress, but I also have the same problem in that the moment move the aperture tab the meter drops to the bottom.

Does anyone have any ideas to why it is doing that? I have no ideas and am stumped as well as shocked that someone else is having the same exact problem.
07-27-2011, 11:08 PM   #13
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With my 6x7, I had the broken chain (since fixed), then the on/off lever on the meter kept working loose and falling off (also fixed), but now I simply hand-meter everything, and no more problems.
07-28-2011, 10:34 AM   #14
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xD I thought about hand metering, but i really want to get the built in meter working. I think there has to be a fix, because I am having the same exact problem as the original poster. i have been threw all he has up until he stopped posting. I just have to wrap my brain around why the needle goes limp after barley moving the aperture ring/lever thing.
08-11-2011, 08:22 PM   #15
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The meter has the A and M mode. These are actually controlled on two circuits it seems. A mode passes a transistor switch and the two potentiometers where as M mode bypasses the aperture side? My TTL had same issues and required the A side Tantalum capacitors to all be replaced. Some versions of the TTL had capacitors that dried out over time.

Last edited by MysteryOnion; 08-28-2011 at 11:04 AM.
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