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Leslie 122xb lower rotor speed issues

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    Leslie 122xb lower rotor speed issues

    I have a 122xb which I use with a Hammond XK3c. I don’t play it that often as I prefer to play my A100s and vintage Leslies, but it may as well work properly - which at the moment, it doesn’t. The problem is this. As soon as I put my foot down on the expression pedal, or turn on the vibrato chorus, or the tube overdrive on the organ, the lower rotor switches to fast and stays there unless I brake to stop completely. Not the horns, just the lower rotor. On advice I’ve replaced the 6550s, but it makes no difference. There are a couple of engineers here in the UK trying to suggest a solution remotely, but to no avail. Has anyone had the same problem and, if so, how did you solve it please?

    Hoping for words of wisdom!
    John
    Hammond A100 1968 (UK manufacture) Leslie 145, Hammond Suzuki XK5 with lower manual and XPK 200 pedalboard, XK3c with lower manual and XPK 200 pedalboard, Leslie 3300, Motionsound Pro 145, modified for 11 pin input and uprated bass driver.

    #2
    My guess would be that the problem is on the motor control board -- perhaps a bad Triac or bad solder joint. Some earlier Leslies with this motor control board have a single-sided board that's prone to cracked solder joints. Later boards have through-plated holes. Through-plated holes are more reliable, but it's a lot harder to remove components without damaging the board. You need excellent soldering tools and skills.

    That's just a guess based on symptoms.
    I'm David. 'Dave' is someone else's name.

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      #3
      Thanks David,

      I'll pass that on to those who may be able to help me actually fix it.
      Hammond A100 1968 (UK manufacture) Leslie 145, Hammond Suzuki XK5 with lower manual and XPK 200 pedalboard, XK3c with lower manual and XPK 200 pedalboard, Leslie 3300, Motionsound Pro 145, modified for 11 pin input and uprated bass driver.

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        #4
        Hello,

        The motor drive of the 122XB is a little bit complicated.
        It consist in a servo loop including a tachometer.
        This is a shutter disk and a fork opto coupler.
        I suggest to clean this opto and the disk for dust and check the disk is secure with the motor.

        Because upper and lower use the same circuit, you can try to swap the fork if it is possible.

        JP

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