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09-25-2011, 02:56 PM   #1
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67 Meter Prism light reading 'drop out'

for some reason my meter gives no reading for 125th as I move the speed from 60 to 125 or 250 to 125. All other readings are fine.

I've removed and re inserted the prism and the lens in the correct sequence and the issue persists. Any ideas for 'probable cause'?

09-25-2011, 05:10 PM   #2
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Interesting... The meter's potentiometer under the shutter speeds has no actual connection to each speed, so it could be that oxidation or dirt is catching it just at that spot. Does it move to another spot when the ASA is adjusted?

Here is a close look...




... observable is the little brushes that rake the continuous contact area.

Last edited by MysteryOnion; 09-25-2011 at 05:16 PM.
09-26-2011, 06:01 AM   #3
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thanks for the reply.

I was having the issue with an ISO/ASA setting of 400 and shutter speed of 125th. Based on your comment, I moved the ISO setting to 100 and the meter reads for 125th but not a 30th. I think you're correct that something like dirt or oxidation at one spot is affecting the brushes that rake the continuous contact area. I've not taken a meter apart and I'd try but I'm wondering if I should or if this should be done by a Pentax techie?

I'm seeing 6 very small 'watchmaker sized' screws holding the cover plate of the meter in place. I also don't see any way to remove the acutal dial above the housing. Is there a guide somewhere to show steps for removal and cleaning this contact point?
09-26-2011, 07:56 AM   #4
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Your obstacles for opening are as follows: (keep track of which is where as a few are differing sizes)
Pin screw holding speed dial
Cross head just next to speed dial
Cross head next to latch on dial side
Cross heads either side to latch on switch side
Cross heads either side of viewfinder
Cross heads hidden under the name badge in front, slowly remove to keep adhesive intact... I have a piece of sticker backing paper for this.

OR

you could just take it to a repair guy?

When opened...
Inspect the potentiometer or called the "Shutter Volume" and use a good audio volume cleaner found at stereo supply (Radio Shack)... try not to over spray.

Small favor... could you give me a snap-shot of the circuit board for your version... I'm studying the differing versions to find out if I could rebuild from a new circuit design as the current three versions encountered so far are each very interesting... yet another crazy project to undertake.


Last edited by MysteryOnion; 09-26-2011 at 08:02 AM.
09-27-2011, 12:14 AM   #5
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thx for the process sequencing.. I'll check to see if I have screw drivers small enough for these phillips heads.. If I get the top off I'll take shots no problem. I enjoy giving people more research info, keeps them busy ;D
09-27-2011, 07:32 AM - 1 Like   #6
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QuoteOriginally posted by jan normandale Quote
I'll check to see if I have screw drivers small enough for these phillips heads..
They aren't Phillips. They are JIS cross-head screws and require special drivers. Use a Phillips and you run the risk of stripping the head. See:

JIS - Japanese Industrial Standard


Steve
09-27-2011, 09:31 AM   #7
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Steve, thanks for the link... now I have to source these specific screwdrivers I guess. I've a question. If you have a 67 and check the screws there is no "dimple" on the screw head to denote the JIS screw as described in the article you linked. So I just want to be sure these are JIS even tho the distinguishing dimple mark is not present. Finally where does one source these drivers in the small size required. Where did you get yours? Thanks!
09-27-2011, 12:34 PM   #8
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I think this is what stevebrot is pointing out... Amazon.com: Screwdriver, JIS Type S Set, 5Pc Magnetic Handle: Home Improvement

Also, I use a set from Wiha and it is seemingly a perfect match with no damage to any of my screws, I will take advantage of stevebrot's reminder and get off my lazyass and pick up a set for the future. Thanks Steve.


Last edited by MysteryOnion; 09-27-2011 at 12:58 PM.
09-28-2011, 12:29 AM   #9
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thx gents... and not too pricey!
09-28-2011, 07:52 AM   #10
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I purchased one of those small screwdriver sets and just ground the Phillips tip down. That seemed to work just fine. But I hear some model airplane hobby stores carry that standard of a screwdriver.
09-28-2011, 09:10 AM   #11
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The Wiha drivers I normally use fits just fine and only a random few sizes are slightly shallow due to how the type of screw or torque limit it is suppose to withstand. The set of run of the mill drivers actually tend to break due to the poor fit. The JIS type look to have the advantage because the are without the shoulders towards center and fit tight against the arms of the cross. The Wiha driver is close and has a slight shoulder to the center and can cause some rounding of the centers which is why some screws fit really snug to the tip and half to be pulled off upon removal from hole. The Moody brand is not too much more than a so called "precision" set of jeweler's set I find and hardware stores or Sears.
09-28-2011, 06:39 PM   #12
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QuoteOriginally posted by tuco Quote
I purchased one of those small screwdriver sets and just ground the Phillips tip down. That seemed to work just fine. But I hear some model airplane hobby stores carry that standard of a screwdriver.
Knowing you online for a couple of years now.... I know you are capable when doing something like this. I don't have a grinder and even if I did... ! It's the line of least resistance to pay $15 +/- for the tool that's appropriate.

;D
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