Luna Pro F always shows max reading

Discussion in 'Camera Building, Repairs & Modification' started by BetterSense, May 23, 2012.

  1. BetterSense

    BetterSense Member

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    I have a Luna Pro F. The battery check works, and the meter appears to work except the needle always pegs all the way to the right. When I press the button, the needle shoots all the way to the right, regardless of the light level. I rotate the dial all the way through its range but the needle stays max'd out. After 30s, the meter turns off like its supposed to.

    It almost seems like the computer dial is completely disconnected or something. Any ideas what can cause this?
     
  2. jordanstarr

    jordanstarr Member

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    Mine did the same. I took the case off and a spring was wrapped around the needle. It was obvious and I placed it in it's right spot and it was back to normal. What likely happened is that it took a bang and the spring just relocated to the other side of the needle and everytime it's engaged, it just swings all the way over. You won't hurt anything by taking off the outer shell and examining it.
     
  3. BetterSense

    BetterSense Member

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    I already took the shell off and made sure that the computer dial is working correctly...it's a 10kohm pot.

    I don't quite understand what could cause what you describe, but I will take another look and maybe it will be clear. The needle does go back down to zero when the meter is off, it just jumps all the way up with any reading.
     
  4. Mick Fagan

    Mick Fagan Subscriber

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    I have the Gossen Profisix, which I believe is the rest of the world version of what you have.

    There is a little green button in the same recess as the big red button, if that is pressed the needle swings straight to the right side of the scale, if the battery is charged and the meter is switched on.

    On the right side of the meter scale is a green rectangle, the needle is supposed to swing to there when the green button is pressed, indicating the level of battery power, or charge.

    Is it possible that the meter has the little green button stuck somehow?

    Mick.
     
  5. BetterSense

    BetterSense Member

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    No; the battery check works fine.

    It's hard to test it, because to turn the meter on you need to press the reading button, and then the needle gets pegged, so you can't tell at that point if the battery check is working. If I wait 30 seconds for the meter to turn off, I'm out of luck because the battery check button doesn't seem to wake it up. But if I put the meter on flash mode, it will turn on without the needle pegging, because it hasn't taken a reading yet. At that point, the battery button works fine. If you actually read a flash exposure with it, the needle pegs the same as when taking an ambient reading.
     
  6. Old-N-Feeble

    Old-N-Feeble Subscriber

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    Mark precisely where the pot is set then take the appropriate tool and turn it back and forth quarter turn. The pot might just be dirty. Be sure to reset it precisely where you made your mark.
     
  7. BetterSense

    BetterSense Member

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    The computer dial, itself, is the 10k pot I was talking about, and I turn that all around and it doesn't make a difference. I also checked it with a multimeter and it works as expected.

    There are like 4 internal pots lined up along the bottom of the circuit board, but I don't know what they all do. I wish I could find a schematic.