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Used Conn 717 organ crackling

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  • Used Conn 717 organ crackling

    Hi! I just picked up a Conn 717 the other day. The flutes have been working great, but the principals, reeds, and strings all sound gritty (excluding pedal stops). They sound decent if I'm only playing one note, but as soon as I play two notes, it beats really bad and sounds really scratchy. I checked the tuning with a free app (not sure how reliable it was) and it looked to be ±2 cents. The owners had it outside for a week before me though. Does anyone know why that would be happening?

    Thank you!

  • #2
    First thing to do is examine the speaker cones for surround rot.
    -Admin

    Allen 965
    Zuma Group Midi Keyboard Encoder
    Zuma Group DM Midi Stop Controller
    Hauptwerk 4.2

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    • #3
      I checked out the all of the speakers, and they looked fine. There are two speakers hooked up to the principal stops, and I heard an identical faint crackling from both of them. Do you know if that would be related?

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      • #4
        You need the service manual, but one may be hard to find. I'd guess that the so-called "pulse" channel (carrying strings, reeds, and diapasons) has a problem. It might be as simple as a dead spot on a thumbwheel pot. Turning the wheel back and forth a few times might clear it up completely. You may be able to locate the audio "mixer" or "level" board with separate thumbwheel pots for flute channel, pulse channel, and perhaps a separate one for the pedals, which may feed into both channels.

        If it's not the pot, it could be an audio cable connector of some kind. The audio inside a Conn or this age is probably not connected using standard RCA plugs and jacks, but probably uses some sort of push-on sleeves that go onto little metal posts. Or the audio going into the amplifier may be carried on some of the pins in a Molex connector. So you'll just have to try to follow the audio signal and find out at what point it gets degraded.

        There is always a chance that you have a faulty amplifier channel or a bad transistor or capacitor in the preamp, but simple mechanical issues are more likely. If there are switches that turn the internal speakers on/off, check those. You might have to clean them or even bypass them.

        Getting one of these 45-year-old organs to work may not be rocket science, but it requires diligence and persistence. So just go to work on it, poking and prodding, pushing and pulling. You may well find a magic spot somewhere that makes it spring to life with a touch. If so, check it out and see what is loose or corroded at that spot.
        John
        ----------
        *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

        https://www.facebook.com/pages/Birds...97551893588434

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        • #5
          Thank you! I tried all the potentiometers I could find, but to no avail. I did find this piece (in picture) in the "Tremolo kill and delay control section". It looks like it's blown, but I don't know if that would affect the entire sound.
          You may only view thumbnails in this gallery. This gallery has 1 photos.

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          • #6
            That capacitor does look shot. I'd replace it and see if it helps. "Tremolo kill and delay" doesn't sound like it would be related to a complete failure of one audio channel, but you never know.
            John
            ----------
            *** Please post your questions about technical service or repair matters ON THE FORUM. Do not send your questions to me or another member by private message. Information shared is for the benefit of the entire organ community, but other folks will not be helped by information we exchange in private messages!

            https://www.facebook.com/pages/Birds...97551893588434

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            • #7
              Interesting corrosion in the vicinity, could be the cause of or collateral damage from the cap failure. I'd definitely try replacing it with an equivalent polymer film cap and make sure all the solder joints on the board are OK.

              Bad solder joints also plagued the output transistor connections in the power amps in these models, which could explain the distortion.

              --- Tom
              Rodgers 660 with additional analog rack sets (practice), 36D/C in digital conversion, Yamaha CVP-107

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