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Thread: Rodgers 990 Stops Issues

  1. #11
    ppp Pianississmo Hurdy Gurdy Man's Avatar
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    I'm back to the misadjusted temperature-compensated power supply! The service manual shows a graph, from which an appropriate voltage can be derived at a particular room temperature. But the graph is not in agreement with the schematic -- 11V versus 13.5V @ 70F -- and neither actually state where the voltage reading should be taken. Is there a more precise procedure by which the power supply voltage can be dialed in? I'm imagining something like "Turn the instrument on and let it stabilize for 30 minutes, then adjust R257 until voltage at the emitter of Q254 is 13.5V." I'm kind of inferring that from the schematic, but there are still too many unknowns. What is actually the correct voltage at 70F? Across which two points should I attach the leads of the DVM? How long should the organ warm up?

  2. #12
    fff Fortississimo toodles's Avatar
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    My drawings indicate voltage should be measured after organ is on for 5 minutes. See the notes above the temperature graph, upper left hand corner or dwg 1396. I have Rev. F.

    I would go by the graph for the voltage, as "-13.5" seems to just be a reference name and what is marked on the board.

    See attached Field Service Bulletin, as it indicates where the voltage should be set.
    Attached Files Attached Files

  3. #13
    ppp Pianississmo Hurdy Gurdy Man's Avatar
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    Thanks, Toodles! That should get me where I need to go.

  4. #14
    ppp Pianississmo Hurdy Gurdy Man's Avatar
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    Beware rebel fighters -- the Rodgers 990 Death Star is fully functional once more!

    I do believe that the catastrophic event was previous repair technicians who ignored the ground warnings. Most of the trouble was in the area with the 15V "ground," so if that was ignored, it would explain a lot of the failures:

    1. Repaired lighted capture system power supply by replacing Q41.
    2. Repaired temperature compensated core memory power supply by replacing Q254 and adjusting voltage per service bulletin.
    3. Replaced 22 bulbs in stops and lighted music rack.
    4. Repaired several stops by replacing SCR Q19.
    5. Convinced 1 1/3 Nineteenth stop to behave by resoldering R311 to great ganging board.

    Mucho gracias to all the Organ Forum folks who helped educate this former Wurlitzer repairman, especially JBird604, Toodles, and Darth-Car himself. The galaxy will never be the same!

  5. #15
    fff Fortississimo toodles's Avatar
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    Glad to know you got it up & running!

  6. #16
    pp Pianissimo Darth-Car's Avatar
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    It truly plays as well as it ever did when it lived at the church. Plus having the instrument in a smaller space allows it to be played at much lower volume levels than those required at the church; subsequently I believe that since the instrument is not working nearly as hard, it has the chance to really create some fantastic analog intonations that would rival even some digital organs of today.
    Until The Next Dimension,
    Admiral Coluch.

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