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Replacing the selenium cell in a Zenit E meter.

Discussion in 'Classic Models & Marques' started by John Farrell, Mar 2, 2021.

  1. John Farrell

    John Farrell Well-Known Member

    Inspired by a recent post on a facebook group, I decided to give this a try, using the cell from a solar powered calculator. I tracked down a suitable donor calculator online, and ordered 5 - they were $1 each (50p in your money).

    IMG_4752s.jpg

    They are simple to dismantle, to remove the solar cell, which isn't soldered in - the connections are glued to the cell.

    IMG_4754s.jpg

    I soldered leads to the cell, and tested the output with a voltmeter.

    IMG_4751s.jpg

    The cell was taller than the original, but not as wide, so I modified the bezel, and put a piece of black card either side.

    IMG_4759s.jpg

    A piece of electrical tape across the back holds everything together, and the bezel fits normally in the camera top plate. IMG_4764s.jpg

    The new cell wired to the meter - I put a 4k7 resistor in series with the cell. IMG_4766s.jpg
     
    Last edited: Mar 2, 2021
    Andrew Flannigan likes this.
  2. steveandthedogs

    steveandthedogs Well-Known Member

    Very impressive bit of work.

    S
     
    John Farrell likes this.
  3. John Farrell

    John Farrell Well-Known Member

    I'm going to experiment with different series resistances, to see if usable light measurements are produced. I have a suspicion that the voltage output of the cell isn't directly proportional to the light falling on it.
     
  4. steveandthedogs

    steveandthedogs Well-Known Member

    Could you compare it with another [working!] meter, one of the type which has a lux scale?

    S
     
  5. John Farrell

    John Farrell Well-Known Member

    I'm going to put another of the solar cells in another dead Zenit (I have a number with dead meters), but have a variable resistor set up rather than a fixed resistor. I'll compare the readings to a working selenium meter.
     
  6. John Farrell

    John Farrell Well-Known Member

    I set up a Zenit E top, with the replacement solar cell, and with flying leads so I could connect a trimpot.

    IMG_4770s.jpg

    It appears, though, that the meter movement in this top has a fault. The results are not promising. The first camera I modified, though, has a lively meter. It underexposes by 2 stops, though, compared to my good selenium meter.
     
  7. John Farrell

    John Farrell Well-Known Member

    I set up an arrangement like the above, with yet another top from a Zenit. The meter on this one gave useable readings, and needed a 50 kilohm resistance to line up with my good selenium meter. It looks like each unit needs the cell to be matched individually to the meter.
     
    Benchista and steveandthedogs like this.
  8. Andrew Flannigan

    Andrew Flannigan Well-Known Member

    That's what miniature presets were invented for but perhaps they were too capitalistic for a Soviet camera! :p
     
    John Farrell likes this.
  9. John Farrell

    John Farrell Well-Known Member

    I did some tests with the working Zenit meter. When the meter reads 1/250 at f8, 100ISO, there is 90mV across the meter. The resistance of the meter is 2.45 Kohms.
     

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