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05-19-2011, 12:32 PM   #1
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Pentax Spotmatic light meter issue

Hi, it's me with my problems with the Spotmatic again. I have bought a camera with an "untested light meter", put a fresh battery in (Renata 1.55V silver oxide I think) and checked it. It is pointing upwards or downwards, depending on the polarity of the battery. My other Spotmatic is working with the same battery, so I am inserting it properly and so on. I think I am prepared to pull out the screwdriver if it is necessary, but I don't know exactly what to look for, so any advice is welcome.

05-19-2011, 12:50 PM   #2
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Is it possible that you have the camera in battery-test mode? To test the battery on a Spotmatic, you set the ASA dial to 100, the shutter speed to 1. Turn the meter on and move the shutter speed to B. If the battery is good, the meter deflects all the way up in the viewfinder.

Simply try the meter at a variety of shutter speeds. If it still does this, then, I'd say there's something wrong with the meter.

My apologies if you already knew this.
05-19-2011, 12:52 PM   #3
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OK, let's say I already knew that
05-19-2011, 09:20 PM   #4
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Contacts under lower cover

Hi, when I inherited my otherwise mint Spotmatic, the meter was totally dead. Even with a new battery. The guy at my local camera store removed the screws holding the bottom plate onto the camera body and showed me a simple pressure contact between the aluminum cover and the camera circuitry. It was ever so slightly corroded.

After a 15 second cleaning of both sides of the contact points with emery paper, he reassembled the camera and the meter works spot-on to this day.

I did the same trick to another well-worn Spotmatic with the same results.

Hope that helps.

05-20-2011, 08:58 AM   #5
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before opening the bottom plate
clean the contacts with the eraser in a pencil first
then check if you need to bend it upwards a bit to make good contact of the battery with the top-cover

check and re-assess
05-21-2011, 08:19 AM   #6
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Well, the battery makes contact, because the needle is moving. The problem is that it is always indicating overexposure.
05-21-2011, 09:57 AM   #7
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QuoteOriginally posted by kcobain1992 Quote
Well, the battery makes contact, because the needle is moving. The problem is that it is always indicating overexposure.
It may be that the wiring has been damaged at some point due to battery leakage. The acids may leach into the wire interior and affect meter functionality. The battery compartment may appear clean, but damage may still remain. This type of damage can be repaired.


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05-21-2011, 10:00 AM   #8
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QuoteOriginally posted by stevebrot Quote
This type of damage can be repaired.
I think you mean "can't"? But if you actually mean what you wrote, then how?

05-21-2011, 10:39 AM   #9
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QuoteOriginally posted by kcobain1992 Quote
I think you mean "can't"? But if you actually mean what you wrote, then how?
I did mean "can". I have a Mamiya/Sekor 1000 DTL that suffered from internal wire corrosion due to a leaking battery. A local technician was able to replace and re-solder the bad wire and connections to restore full meter functionality. Most older cameras (my Mamiya is the same vintage as your Spottie) have very simple electronics and can be repaired by anyone having the proper tools and access to parts and an understanding of how the meter works.


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05-29-2011, 11:22 PM   #10
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Commonly when a spotmatic meter needle pegs one way or the other it is because of damaged wiring. When you remove the top cover there is a black wire and a yellow wire that go from where the meter circuit board is to where the shutter dial is. Sometimes when a camera is dropped the top cover bends in enough to sever one or both of the wires. Surprisingly this has been a more common problem than a bad ammeter (meter needle) in my experience. If you decide to remove the top cover remember that the screw that holds the counter dial on is left-hand thread. I guess you will also need to buy a spanner wrench from Micro-tools.com. etc. ......
05-31-2011, 07:24 AM   #11
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There is no ding on the camera so I don't think it has ever been dropped.
05-31-2011, 07:46 AM   #12
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I have an early model spotmatic that I thought had an inaccurate meter. After playing with it I noticed that the meter needle moved in the direction opposite of where it should when making exposure adjustments. I surmised that the original mercury cell battery must be of an opposite polarity that the silver oxide battery I had in it. I placed tape over the flat side of the battery (so it wont short out), I cut a small hole in the center of the tape, and I inserted the battery upside down. It works perfectly and the meter is now dead on accurate. I don't know if I'm correct in assuming that the spotmatic uses a battery that is reversed in polarity, but the approach I took worked for me. Good luck.
05-31-2011, 07:49 AM   #13
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Yes, if I reverse the polarity of the battery, it is pointing constantly downwards. I have said that before though.
10-01-2011, 10:19 AM   #14
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I'm back with a set of questions again. I disassembled the film rewind knob knowing that under that thing there should be a potentiometer to adjust the light meter's sensitivity, but for the life of me I can't find it (or maybe I don't know what I'm looking at). I have read on another forum (can't find the link now), that while the Spotmatic uses 2 light cells for balancing voltages of different batteries, it can as well function with only one light cell if it is properly calibrated. Now, I don't know if this is true or how do the light cells actually look, but it certainly sounds plausible and is likely the cause that my camera currently shows overexposure. So if you ever adjusted the light meter, please, please tell me where to look for the pot!

10-01-2011, 12:47 PM   #15
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The pot is a flat, minature control under the wires through the round hole. Needs a tiny screwdriver to fit the center slot.
The balanced circuit on the Spotmatic isn't based on the 2 photocells, but on the circuit design. The 2 cells are needed to properly center-weight the reading. If one cell is bad you won't be able to adjust the meter to be linear over the range. Commonly the cells fail by lowering the "dark" resistance so that the meter will underexpose in dim light. You need to remove the top cover to get access to the cells (at the sides of the eyepiece) and check the resistance of each. I've repaired a couple by buying junk bodies and finding good cells from them.
Sometimes the pots and switch contacts also get dirty and need to be cleaned with a good contact cleaner.
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