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Thread: Leslie 771 schematic

  1. #1
    ff Fortissimo muckelroy's Avatar
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    Leslie 771 schematic

    Anyone?

    Can't seem to find this one anywhere. When was this produced? People say it's similar to the 770, but how similar is it?

  2. #2
    ff Fortissimo Hamman's Avatar
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    Its not a 971??
    Allen 5300-DK, Hammond A-105, Conn Custom 905-DK

  3. #3
    ff Fortissimo picothinker's Avatar
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    According to Captain Foldback, a 771 is "Updated version of model 770, produced by Hammond-Suzuki from about 1991. In 2006, the even more powerful (300W) model 971 was introduced."

    Below is a schematic for a 770, and Captain Foldback has the 760/770 service manual here.

    373028-1.jpg

    I finally found some info on the 771 here, but only a 'brochure page' on archive.org. Looks like it is a bi-amped Leslie, with two amps. From the looks of the 770 schematic, looks like it was bi-amped as well, so hopefully that will be helpful.

  4. #4
    ff Fortissimo muckelroy's Avatar
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    You got a few steps further than I did!! I appreciate the digging. Y'all are awesome.

  5. #5
    ff Fortissimo muckelroy's Avatar
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    I'm digging up this thread from the grave, because the very same Leslie that started this thread has taken up residence with a new owner, and they're asking me for help. I have not seen the Leslie in person yet.

    The Leslie has an 11-pin connection. It's connected to a TrekII UC1-a pedal. The TrekII UC1-a is fed by an M-111 organ, which has a TrekII OBL-2 line out in use.

    The 771 cabinet has modern-day motors (the speed-controller board variety as you'd find in the 122A, etc.) Because it uses the 11-pin interface, it has a dedicated AC power cable.

    Therefore, I have little faith that the Leslie 760 schematics will do any good here, unless it truly is a re-hash of that design with an 11-pin front-end, and a motor speed control board.

    What are the issues you ask?
    1. No upper rotor movement on fast. When switching to slow, the horn spins fast for a couple seconds, then stops again.
    (Bad motor? Maybe. Problem with control board? also likely.)
    2.) No audio. Crackled / distorted audio comes through when playing very loudly.

    I'll reach out to Hammond Suzuki proper to see about getting schematics.

  6. #6
    ff Fortissimo muckelroy's Avatar
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    I have schematics from Hammond Suzuki. I can post them on the files page later, I suppose.

    After consulting many resources (both documents and talented / generous people,) I have a much better understanding of how this thing works. What confused me at first was the role of pin 6. Pin 6 is the control voltage that ultimately tells the Leslie to power itself on. Connecting pin 6 to pin 5 will cause the control voltage to go to zero, which makes the Leslie turn on. The UC-1A doesn't do this connection mechanically, but via some diodes / transistors.

    The symptoms this Leslie is having make it seem that the 11-pin cable is shoved in the wrong way. As though the tremolo switch was interacting with pin 6/7 instead of pins 7/8. Alas the owner confirms this is NOT the cause, and the cables are seated with the correct orientation. No easy fixes for me today.

    I might be looking at this Leslie over the weekend.

  7. #7
    ff Fortissimo muckelroy's Avatar
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    The issue was that the 11 pin cable was misaligned. Index tab broke off. Aligned correctly, all good. Will mark it and replace the connector on my next visit.

    Leslie sounds great! Didn’t need a bit of work otherwise. Oiled the upper rotor.

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