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  1. #1

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    Beseler Enlarger Timer - How to Calibrate?

    I have a Beseler Audible/Repeating Englarging Timer that is slightly off. If I set it to 20 seconds, I check it against a good stop watch and it only runs about 17 seconds. The audible beeps seem to be correct though. In any event, I took the back panel off and there are what look to be 3 variable resistors labeled R7, R10 and R20. I take it that I can adjust this device moving these a bit. Before I just randomly start fiddling with this, does anyone know which one would help my timing problem?

    As I don't see a model number on this, I will describe it. It is a basically rectangular black box, about 6.5 x 6 x 2 inches, 2 big dials for seconds and tenths of seconds, a 10x multiplying switch, red focus off time switch and rectangular print button. A pretty standard unit a few years ago.

    Thanks

    Dave

  2. #2

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    Dave,

    Is accuracy that important to you?

    Consistency in an enlarger timer is way more important.

    Mike

  3. #3

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    I understand your point, but yes, I suppose it is. I want to be able to record times and be able to use any timer in the future and get it right.

  4. #4
    Rick A's Avatar
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    If it is consistant, you can still record your times, they will always(unless it goes off-kilter) be what they are. If, when you set it to 20 ceconds, and get the exposure you like, then keep using that setting. It doesn't matter if it is really not exactly 20 seconds. As mpirie states, consistancy is more important. I have several timers, and all are calibrated to each other, and thats all that I care about. I have settings that I know the results of, and are repeatable.
    Rick A
    Argentum aevum
    BTW: the big kid in my avatar is my hero, my son, who proudly serves us in the Navy. "SALUTE"

  5. #5

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    Rick, yes, I understand, but the other timers I have seem to be accurate, hence my original question.

  6. #6

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    Now you know why I'm so enamored of my old GraLab and Time-O-Lite timers. Both are driven by electric clockworks with motors whose speed is controlled by the frequency of the AC current. Voltage may vary, but the frequency is very tightly controlled and these things don't drift. The Time-O-Lite is repeatable, the GraLab is not; but it can accommodate a footswitch.
    Frank Schifano

  7. #7

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    There will be a chrystal oscillator in any digital timer. If you have been living right, there will be a trimmer capacitor very near the chrystal itself. If you haven't you will have to add capacitance to the circuit a pico farad or so at the time. Note to slow the oscillator (which you want to do) you must add capacitance.

  8. #8

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    When you took the back cover off, what did you see? Did you see a large number of registers either on the printed circuit board or around switches? Or, did you see just few IC chips and some analog circuitry? Just because it has dials and numbers, I wouldn't automatically assume it's digital in a sense it has a master oscillator for 1 second, and cascaded counter counts up the preset intervals. It could very well be an adjustable timer with registers to set the timing.

    I say this because if it was entirely digital, there will be little need for trim pots like OP says.
    Develop, stop, fix.... wait.... where's my film?

  9. #9
    ic-racer's Avatar
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    Hard to know without some pictures or a schematic. The good old Omega timer has only resistors and capacitors and a single SCR and a single trimpot.

  10. #10

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    Okay, here are some pictures!

    The front:



    Opening the back where you will notice that they made the circuit board so that these variable resistors (that is what I am calling them, I may be wrong) are easy to access as there is a hole in the board at each of these points. They are located in the lower middle, lower right corner and above that corner:



    And then finally, the front side of the circuit board (you will notice R20 the mid left side, R7 below that in the lower left corner and R10 in the middle of the bottom edge.



    Any ideas?

    Dave
    Last edited by gkardmw; 06-23-2010 at 07:20 PM. Click to view previous post history. Reason: Correcting picture

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