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10-22-2012, 11:07 PM   #1
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Wonky 645 Meter

Picked up a 645 in the local classifieds for $700, came with 45mm f/2.8, 75mm f/2.8, and 120mm f/4 Macro, 4 backs, 2 battery holders, and 23 rolls of 220!

All is well except my camera will not meter properly in any auto mode, no matter what lighting I am in. It thinks it will always overexpose - it flashes 1/1000 f/22 in the viewfinder. If I drop the ISO to 6 and put on a lens cap I can sometimes get it down to 1/1000 f/19. This is with new, fresh alkaline batteries.

Has anyone encountered a faulty meter like this? If so, have you managed to fix it?
It's a long shot, but I am hoping for a quick fix, I don't really want to send it in to Pentax for repair. (if they still fix it)

Overall, it is not so bad...I have managed to make it "work" in metered manual mode by inputting the ISO 4 stops slower than the film speed. (calibrated against my K-5)
However, the meter only reads an accurate exposure as if the lens were wide open. In other words, 1/125s f/2.8 will meter "OK" just as well as 1/125s f/22.
When I stop down the aperture I must remember to adjust the shutter speed accordingly before shooting.

Any help is appreciated!

10-23-2012, 11:55 PM   #2
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People who may know will need to know which 645 you have (645, 645N, 645N II).
10-30-2012, 06:14 PM   #3
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Well, if it were a 645N, 645NII, or 645D, I would have written one of those things. The lack of any letters or roman numerals should be understood quite readily I should think.
10-31-2012, 04:42 PM   #4
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Very frustrating, especially as so far no-one seems able to help. It sounds as if a repairer's help is needed.It doesn't sound simple like a tweak of the controls or cleaning electrical contacts. If you were in the U.K I could recommend at least one very competent repairer and I am sure there are others but as you are in Canada that's not practical.

Hopefully someone will be able to help.


10-31-2012, 06:16 PM - 1 Like   #5
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Well, I wanted to stay out of suggesting anything as I have yet to win a broken 645 at auction so as to it take apart...however, my 2 cents worth is this...

The thing that comes to mind first off is if the push button method of setting speeds relies on a usual memory function.
The pressing of the release button to activate the meter for displaying prior to shooting the picture is not matching the recorded setting that was gathered just a fraction of the second prior to starting the cycle of raising the mirror and opening the curtain.
It seems the first place I would check is the contacts running to and from the release switch and check if the mirror box if it has a contact switch that must be set to confirm the sequence was started properly prior to the mirror going up.
Some contacts do get a little oxidized or even gummed up over time. The other factor is how the control panel buttons are wired and if the connections are soldered or clipped in place and if one of the connections is not communicating well... i.e...a steady pulse at a know value would be computed as 1/250th, but a irregular pulse of the same value might be computed as 1/15th.

This of course is not a spray it and see issue. The repair manual and some familiarity with camera repair is needed.
11-01-2012, 05:46 PM   #6
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Thanks for your input, MysteryOnion. To be honest, most of what you wrote flew over my head.
Setting shutter speeds works fine, I can get proper exposures reliably, and I do get under or over exposure indication in metered manual mode (lens wide open) when the shutter speed is set off zero. Actual timing of the shutter speeds seems accurate too, I think the issue is aperture specific.

It seems to me (warning: unprofessional opinion) the aperture-lever mechanism camera-side is not making physical contact with whatever circuit it is tied to, which might explain the wide-open metering issue in manual mode. The meter will read wide open because the mechanical linkages have physically opened the aperture all the way, but the camera electronics don't know the stopped-down aperture.

It just seems counter-intuitive that with the lens in "A" setting the meter reads massive overexposure instead of underexposure, much more over-exposure than the 4-stops I have to use to compensate in metered-manual.
It is so much over-exposure I think the camera is calculating backwards - calculating an exposure value 10 stops MORE than wide open. (6 stops lens range assuming f/2.8-22 + 4 built in the meter)
The reason why this could happen eludes me.

Something else of note: When shooting in Aperture-Priority Auto mode the lens does not shoot at the correct electronically-selected aperture, only f/22. I'll enter 2.8 and the lens will close all the way down at exposure.

Looks like I might have to send it in. Shame to be without it for 4-6 weeks, and I fear the estimate will be astronomical.

I would poke around and attempt repair myself if I had a service manual, but as it is I don't even know how to crack it open properly.

Thanks again everybody!

Last edited by Mock; 11-01-2012 at 06:03 PM.

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